EX-4.1





 Exhibit 4.1 

EXECUTION VERSION 

SECURITIES PURCHASE AGREEMENT 

This SECURITIES PURCHASE AGREEMENT (this “Agreement”) is made and entered into as of December 6, 2019 by and among
Summit Therapeutics plc, a public limited company incorporated in England and Wales with the Registrar of Companies of England and Wales, with its principal place of business at 136a Eastern Avenue, Milton Park, Abingdon, Oxfordshire OX14 4SB,
United Kingdom (the “Company”), and the investor named on Exhibit A hereto (the “Investor”). 

RECITALS 
 A. The Company
and the Investor are executing and delivering this Agreement in reliance upon the exemption from securities registration afforded by the provisions of Regulation D, as promulgated by the U.S. Securities and Exchange Commission (the
“SEC”) under the Securities Act of 1933, as amended; 
 B. The Investor wishes to purchase from the Company, and the Company
wishes to sell and issue to the Investor, upon the terms and subject to the conditions stated in this Agreement, (i) ordinary shares, with a nominal value of £0.01 per share, of the Company (the “Ordinary Shares”) and
(ii) certain warrants to subscribe for Ordinary Shares pursuant to the warrant instrument to be executed by the Company in the form attached hereto as Exhibit B (the “Warrant Instrument”) (each, warrant under the Warrant
Instrument a “Warrant” and collectively, the “Warrants”); 
 C. On or prior to the date hereof, the parties
hereto and Cairn Financial Advisers LLP have executed and delivered a deed of termination (the “Deed of Termination”) to terminate that certain Relationship Agreement (the “Relationship Agreement”), dated as of
December 14, 2018, by and among the Company, the Investor and Cairn Financial Advisers LLP, which shall be conditional upon, and shall take effect upon, the cancellation of trading of the Ordinary Shares on AIM (as defined below) becoming
effective by way of the issue by the London Stock Exchange plc of a dealing notice (as such term is defined in the AIM Rules (as defined below)) (such effectiveness of cancellation, the “Termination Condition”); and 

D. The Investor acknowledges that upon completion of the acquisition of the Purchased Securities pursuant to this Agreement, the Investor will
continue to be subject to certain U.K. regulatory obligations including, amongst others, pursuant to the City Code and the Disclosure Guidance and Transparency Rules of the U.K. Financial Conduct Authority. 

In consideration of the mutual promises made herein and for other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows: 
 1. Definitions. For the purposes of this Agreement, the following terms
shall have the meanings set forth below: 
 “Admission” means admission of the Purchased Ordinary Shares to trading on AIM
pursuant to Rule 6 of the AIM Rules. 
 “ADSs” means American Depositary Shares, each representing five (5) Ordinary
Shares. 
  












 “Affiliate” means, with respect to any Person, any other Person which
directly or indirectly through one or more intermediaries controls, is controlled by, or is under common control with, such Person. A Person shall be deemed to control another Person if such Person possesses, directly or indirectly, the power to
direct or cause the direction of the management and policies of such Person, whether through the ownership of voting securities, by contract or otherwise. Without limiting the generality of the foregoing, a Person shall be deemed to control another
Person if any of the following conditions is met: (i) in the case of corporate entities, direct or indirect ownership of more than fifty percent (50%) of the stock or shares having the right to vote for the election of directors, and
(ii) in the case of non-corporate entities, direct or indirect ownership of more than fifty percent (50%) of the equity interest with the power to direct the management and policies of such non-corporate entities. 
 “Aggregate Purchase Price” has the meaning set forth in
Section 2. 
 “Agreement” has the meaning set forth in the preamble to this Agreement. 

“AIM” has the meaning set forth in Section 4.12(e). 

“AIM Documents” means the documents made publicly available by the Company by way of announcement via a Regulatory
Information Service prior to the date hereof. 
 “AIM Rules” means the AIM Rules for Companies as published from time to
time by London Stock Exchange plc. 
 “Appointment” shall mean the appointment of the Director Nominees to the
Company’s Board of Directors. 
 “Business Day” means a day, other than a Saturday, Sunday or United Kingdom public
holiday, on which banks in New York City are open for the general transaction of business. 
 “City Code” shall mean the
City Code on Takeovers and Mergers as promulgated from time to time by the Panel on Takeovers and Mergers. 
 “Closing” has
the meaning set forth in Section 3.1. 
 “Closing Date” has the meaning set forth in Section 3.1. 

“Company” has the meaning set forth in the preamble to this Agreement. 

“Company SEC Documents” has the meaning set forth in Section 4.12(a). 

“Deed of Termination” has the meaning set forth in the recitals to this Agreement. 

“Delisting Approval” means all necessary approvals of the Company’s shareholders required to be obtained in relation to
the consummation of the cancellation of trading of the Ordinary Shares on AIM. 
 “Director Nominees” shall mean
Dr. Elaine Stracker, Dr. Ventzislav Stefanov, Manmeet Soni and the Investor. 

  
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 “Disposition” or “Dispose of” shall mean any
(i) pledge, sale, contract to sell, sale of any option or contract to purchase, purchase of any option or contract to sell, grant of any option, right or warrant for the sale of, or other disposition of or transfer of any ADSs, Ordinary Shares,
or any Ordinary Share Equivalents, including, without limitation, any “short sale” or similar arrangement, or (ii) swap or any other agreement or any transaction that transfers, in whole or in part, directly or indirectly, the
economic consequence of ownership of the ADSs or the Ordinary Shares, whether any such swap or transaction is to be settled by delivery of securities, in cash or otherwise. 

“Enforceability Exceptions” has the meaning set forth in Section 4.4(b). 

“Governmental Authority” shall mean any court, agency, authority, department, regulatory body or other instrumentality of any
government or country or of any national, federal, state, provincial, regional, county, city or other political subdivision of any such government or country or any supranational organization of which any such country is a member. 

“Group” means the Company and its subsidiary undertakings (and “Group Company” shall be construed
accordingly). 
 “IFRS” has the meaning set forth in Section 4.12(d). 

“Investor” has the meaning set forth in the preamble to this Agreement. 

“Law” or “Laws” shall mean all laws, statutes, rules, regulations, orders, judgments, injunctions and/or
ordinances of any Governmental Authority. 
 “Material Adverse Effect” means a material adverse effect on (i) the
assets, liabilities, results of operations, financial condition or business of the Company and its subsidiaries taken as a whole, (ii) the legality or enforceability of this Agreement or (iii) the ability of the Company to perform its
obligations under this Agreement. 
 “Nasdaq” means The Nasdaq Stock Market. 

“Ordinary Share Equivalents” shall mean any options, warrants or other securities or rights convertible into or exercisable
or exchangeable for, whether directly or following conversion into or exercise or exchange for other options, warrants or other securities or rights, Ordinary Shares of the Company, including those represented by ADSs, or any swap, hedge or similar
agreement or arrangement that transfers in whole or in part, the economic risk of ownership of, or voting or other rights of, the Ordinary Shares. 

“Ordinary Shares” has the meaning set forth in the recitals to this Agreement. 

“Person” means an individual, corporation, partnership, limited liability company, trust, business trust, association, joint
stock company, joint venture, sole proprietorship, unincorporated organization, Governmental Authority or any other form of entity not specifically listed herein. 

“Placing” means the concurrent placing of Ordinary Shares and Warrants to investors outside of the United States pursuant to
an exemption from registration under Section 4(a)(2) of the 1933 Act and Regulation S under the 1933 Act. 

  
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 “Press Release” has the meaning set forth in Section 10.7. 

“Purchased Ordinary Shares” has the meaning set forth in Section 2. 

“Purchased Securities” has the meaning set forth in Section 2. 

“Purchased Warrants” has the meaning set forth in Section 2. 

“Registrar” means Link Asset Services, a trading name for Link Market Services Limited, being the Company’s registrar,
or such other registrar as the Company may appoint from time to time. 
 “Registration Rights Agreement” means the
Registration Rights Agreement, dated as of January 9, 2019, by and between the Company and the Investor. 
 “Regulatory
Information Service” shall have the same meaning set forth in the AIM Rules. 
 “Relationship Agreement” has the
meaning set forth in the recitals to this Agreement. 
 “Relevant Accounting Standards” shall mean generally accepted
United Kingdom accounting policies, practices, principles and conventions using all relevant International Financial Reporting Standards as adopted by the European Union, including all IFRS, International Accounting Standards, Interpretations issued
by the International Financial Reporting Interpretations Committee and the Standing Interpretations Committee and all relevant statements and recommendations from professional accountancy bodies. 

“Resignation” shall mean the resignations of each of the Resigning Directors from the Company’s Board of Directors. 

“Resigning Directors” shall mean Frank Armstrong, Leopoldo Zambeletti and David Wurzer, each of whom are members of the
Company’s Board of Directors as of the date of this Agreement. 
 “Sarbanes-Oxley Act” has the meaning set forth in
Section 4.12(g). 
 “SEC” has the meaning set forth in the recitals to this Agreement. 

“Shareholder Approval” means all necessary approvals of the Company’s shareholders required to be obtained in relation
to the consummation of the transactions contemplated by the Transaction Documents, including without limitation the Delisting Approval. 

“Shareholder Circular” means the circular (including the appended notice of general meeting) to be circulated by the Company
to its shareholders in connection with the Shareholder Approval and which is in the form attached as Exhibit G hereto. 

“Shareholders’ Meeting” has the meaning set forth in Section 7.3. 

“Short Sales” means all “short sales” as defined in Rule 200 of Regulation SHO under the 1934 Act (but shall not be
deemed to include the location and/or reservation of borrowable Ordinary Shares or ADSs). 

  
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 “Termination Condition” has the meaning set forth in the recitals to this
Agreement. 
 “Third Party” shall mean any Person, including a Governmental Authority, other than the Investor, the Company
or any Affiliate of the Investor or the Company or any of their respective representatives. 
 “Trading Day” shall mean a
day on which trading in the Ordinary Shares generally occurs on AIM. 
 “Transaction Documents” means this Agreement, the
Warrant Instrument and the Shareholder Circular. 
 “Warrant” or “Warrants” has the meaning set forth in
the recitals to this Agreement. 
 “Warrant Instrument” has the meaning set forth in the recitals to this Agreement. 

“Warrant Shares” means the Ordinary Shares issuable upon exercise of the Purchased Warrants. 

“1933 Act” means the Securities Act of 1933, as amended, or any successor statute, and the rules and regulations promulgated
thereunder. 
 “1934 Act” means the Securities Exchange Act of 1934, as amended, or any successor statute, and the rules
and regulations promulgated thereunder. 
 “6-K Filing” has the meaning set forth
in Section 10.7. 
 2. Purchase and Sale of the Ordinary Shares and Warrants. Subject to the terms and conditions of this
Agreement, at the Closing, the Company shall issue and sell to the Investor, and the Investor shall purchase from the Company, (i) 166,157,050 Ordinary Shares (the “Purchased Ordinary Shares”) and (ii) 24,923,555 Warrants each
entitling the Investor to purchase one Ordinary Share (the “Purchased Warrants” and together with the Purchased Ordinary Shares, the “Purchased Securities”), for an aggregate purchase price of $47,371,000 (the
“Aggregate Purchase Price”). The Purchased Warrants shall have an exercise price equal to £0.243 per Warrant (subject to adjustment as provided therein). 

3. Closing. 
 3.1. The
completion of the purchase and sale of the Purchased Securities (the “Closing”) shall occur automatically upon Admission (the “Closing Date”), provided that all of the conditions set forth in Section 6 shall
have been (or shall be, as the case may be) satisfied or (where capable of waiver) waived at such time. The Closing shall occur remotely on the Closing Date via exchange of documents and signatures or at such place as the Company and the Investor
may agree in writing. 
 3.2. Following the attainment of the Shareholder Approval and by not later than the Business Day immediately prior
to the Closing Date, the Investor shall deliver or cause to be delivered to the Company the Aggregate Purchase Price via wire transfer of immediately available funds pursuant to the wire instructions delivered to the Investor by the Company after
the date of this Agreement. At the Closing, the Company shall deliver or cause to be delivered the Purchased Securities to the Investor. If the Closing has not occurred within two Business Days immediately following the date that the Aggregate


  
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Purchase Price has been delivered to the Company pursuant to this Section 3.2, then, unless the Investor shall provide otherwise in writing, the Company shall return the Aggregate Purchase
Price funds so received to the Investor no later than the third Business Day following the Company’s receipt of such funds. The Company shall not spend or commit to spend any of the Aggregate Purchase Price funds received hereunder prior to the
Closing and the Resignation and Appointment. 
 4. Representations and Warranties of the Company. The Company hereby represents and
warrants to the Investor that, except as otherwise described in this Agreement, the Company SEC Documents and/or the AIM Documents, which qualify these representations and warranties in their entirety: 

4.1. Organization, Good Standing and Qualification. The Company has been duly organized and is validly existing and in good standing
under the laws of its jurisdiction of organization, is duly qualified to do business and is in good standing in each jurisdiction in which its ownership or lease of property or the conduct of its businesses requires such qualification, and has all
power and authority necessary to own or hold its properties and to conduct the businesses in which it is engaged, except where the failure to be so qualified or in good standing or have such power or authority would not, individually or in the
aggregate, have a Material Adverse Effect. 
 4.2. Capitalization and Voting Rights. 

(a) As of October 31, 2019, the issued share capital of the Company consists of 160,494,758 Ordinary Shares. The Company has also
(i) granted outstanding options under the Company’s equity incentive plans over, in aggregate, 19,810,536 Ordinary Shares, (ii) granted restricted stock units under the Company’s directors’ remuneration policy over 709,379
Ordinary Shares and (iii) issued warrants for the purchase of nil Ordinary Shares, which are outstanding as of October 31, 2019. The issued share capital of the Company has been validly allotted and issued under due authority and is fully
paid. 
 (b) Except as described or referred to in Section 4.2(a) above, arising pursuant to or referred to in the Transaction Documents
or arising pursuant to the Placing, as of the date of this Agreement, there are no outstanding rights (including, without limitation, pre-emptive rights), warrants or options to acquire, or instruments
convertible into or exchangeable for, any share capital or other equity interest in the Company, or any contract, commitment, agreement, understanding or arrangement of any kind relating to the issuance of any share capital of the Company, any such
convertible or exchangeable securities or any such rights, warrants or options. 
 (c) Except as arising pursuant to the Registration Rights
Agreement, no Person has any right to cause the Company to effect the registration under the 1933 Act of any securities of the Company. 

(d) Except for the Relationship Agreement, the Company is not a party to or subject to any agreement or understanding relating to the voting of
share capital of the Company or the giving of written consents by a stockholder or director of the Company. On or prior to the date hereof, the Company has executed the Deed of Termination in order to terminate the Relationship Agreement upon the
Termination Condition being met. 

  
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 (e) If the Company obtains the Shareholder Approval, the execution and delivery of this
Agreement and the Warrant Instrument, and the transactions contemplated by the Transaction Documents, will not result in the triggering of any anti-dilution rights, or otherwise increase the number of Ordinary Shares issuable or decrease the
exercise or conversion price, under any warrant, option, convertible note or other instruments convertible or exchangeable for, any share capital or other equity interests in the Company (except for the issuance of the Purchased Securities and the
Warrant Shares and the issuance of Ordinary Shares in the Placing and Ordinary Shares issuable upon exercise of the Warrants). 
 4.3.
Subsidiaries. All the outstanding share capital or other equity interests of each subsidiary owned, directly or indirectly, by the Company have been duly authorized and validly issued, are fully paid and are owned directly or indirectly by
the Company, free and clear of any lien, charge, encumbrance, security interest, restriction on voting or transfer or any other claim of any third party. 

4.4. Authorization. 
 (a)
The Company has the requisite corporate power and authority to execute and deliver this Agreement and (subject to the satisfaction of the conditions to Closing) to perform its obligations hereunder; and all action required to be taken (including
unanimous approval of the Company’s Board of Directors) for the due and proper authorization, execution and delivery by it of this Agreement and (subject to the satisfaction of the conditions to Closing) the consummation by it of the
transactions contemplated hereby has been duly and validly taken. Upon execution and delivery of the Warrant Instrument, the Company will have the requisite corporate power and authority to execute and deliver such agreement and to perform its
obligations thereunder; and all action required to be taken (including unanimous approval of the Company’s Board of Directors) for the due and proper authorization, execution and delivery by it of such agreement and the consummation by it of
the transactions contemplated thereby will have been duly and validly taken. 
 (b) This Agreement has been, and upon the execution and
delivery of the Warrant Instrument, each such agreement will be, duly executed and delivered by the Company, and this Agreement constitutes, and upon execution and delivery of the Warrant Instrument, each such agreement will constitute, a valid and
legally binding obligation of the Company, enforceable against the Company in accordance with their respective terms, except as enforceability may be limited by applicable bankruptcy, insolvency or similar laws affecting creditors’ rights
generally or by equitable principles relating to enforceability (collectively, the “Enforceability Exceptions”). 
 (c) No
stop order or suspension of trading of the Company’s equity securities has been imposed by AIM, Nasdaq, the SEC or any other Governmental Authority and remains in effect. 

4.5. No Defaults. The Company is not (i) in violation of articles of association or similar organizational documents; (ii) in
default, and no event has occurred that, with notice or lapse of time or both, would constitute such a default, in the due performance or observance of any term, covenant or condition contained in any indenture, mortgage or loan agreement to which
the Company is a party or by which the Company is bound or to which any of the property or assets of the Company is subject; (iii) in default, and no event has occurred that, with notice or lapse of time or both, would constitute such a
default, in the due performance or observance of any term, covenant or condition contained in 

  
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any deed of trust or other agreement or instrument to which the Company is a party or by which the Company is bound or to which any of the property or assets of the Company is subject (except for
any agreements referred to in clause (ii) above); or (iv) in violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority having jurisdiction over the Company
or any of its subsidiaries, except, in the case of clauses (iii) and (iv) above, for any such default or violation that would not, individually or in the aggregate, have a Material Adverse Effect. 

4.6. No Conflicts. The execution, delivery and (subject to the satisfaction of the conditions to Closing) performance of this Agreement
and the Warrant Instrument, the issuance and sale of the Purchased Securities and the Warrant Shares and the consummation of the transactions contemplated by the Transaction Documents will not (i) conflict with or result in a breach or
violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company pursuant to, any indenture, mortgage or loan
agreement to which the Company is a party or by which the Company is bound or to which any of the property or assets of the Company is subject, (ii) conflict with or result in a breach or violation of any of the terms or provisions of, or
constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company pursuant to, any deed of trust or other agreement or instrument to which the Company is a party or by
which the Company is bound or to which any of the property or assets of the Company is subject (except for any agreements referred to in clause (i) above), (iii) result in any violation of the provisions of the articles of association or
similar organizational documents of the Company or (iv) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority having jurisdiction over the
Company or any of its subsidiaries, except, in the case of clauses (ii) and (iv) above, for any such conflict, breach, violation or default that would not, individually or in the aggregate, have a Material Adverse Effect. 

4.7. No Governmental Authority or Consents. No consent, approval, authorization, order, license, registration or qualification of or
with any court or arbitrator, governmental or regulatory authority is required for the execution, delivery and (subject to the satisfaction of the conditions to Closing) performance by the Company of this Agreement, or the Warrant Instrument, or
(subject to the satisfaction of the conditions to Closing) the issuance and sale of the Purchased Securities and the Warrant Shares, except such filings as may be required to be made with the SEC or under any state securities laws, foreign
securities laws, blue sky laws, the United Kingdom Companies Act 2006, or the rules and regulations of Nasdaq, the London Stock Exchange plc or AIM, which filings shall be made in a timely manner in accordance with all applicable Laws. 

4.8. Valid Issuance of Purchased Securities and Warrant Shares. When issued, sold and delivered at the Closing in accordance with the
terms hereof for the Aggregate Purchase Price and subject to the satisfaction of the conditions to Closing, the Purchased Ordinary Shares shall be duly authorized, validly issued and fully paid, free from any liens, encumbrances or restrictions on
transfer, including preemptive rights, rights of first refusal or other similar rights, and shall rank pari passu with all Ordinary Shares outstanding as of the date of this Agreement, other than as arising pursuant to this Agreement, as a
result of any action by the Investor or under U.K. securities Laws or U.S. federal or state securities Laws. When issued, sold and delivered at the Closing in accordance with the terms hereof for the Aggregate Purchase Price and subject to the
satisfaction of the conditions to Closing, the 

  
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Purchased Warrants shall be duly authorized, validly issued and fully paid, and the Warrant Shares shall be reserved for issuance. Upon exercise of the Purchased Warrants in accordance with their
terms, including the payment of any exercise price therefor, the Warrant Shares shall be duly authorized, validly issued and fully paid, free from any liens, encumbrances or restrictions on transfer, including preemptive rights, rights of first
refusal or other similar rights, and shall rank pari passu with all Ordinary Shares outstanding as of the date of this Agreement, other than as arising pursuant to this Agreement, as a result of any action by the Investor or under U.K.
securities Laws or U.S. federal or state securities Laws. 
 4.9. Litigation. There are no legal, governmental or regulatory
investigations, actions, suits or proceedings pending to which the Company or any of its subsidiaries is a party or to which any property of the Company or any of its subsidiaries is subject that, individually or in the aggregate, would reasonably
be expected to have a Material Adverse Effect; and no such investigations, actions, suits or proceedings are threatened or, to the knowledge of the Company, contemplated by any governmental or regulatory authority or threatened by others. 

4.10. Licenses and Other Rights; Compliance with Laws. The Company and its subsidiaries possess or are in the process of obtaining all
licenses, certificates, permits and other authorizations issued by, and have made all declarations and filings with, the appropriate federal, state, local or foreign governmental or regulatory authorities that are necessary for the ownership or
lease of their respective properties or the conduct of their respective businesses as described in the Company SEC Documents, except where the failure to possess or make the same would not, individually or in the aggregate, have a Material Adverse
Effect; and neither the Company nor any of its subsidiaries has received notice of any revocation or modification of any such license, certificate, permit or authorization or has any reason to believe that any such license, certificate, permit or
authorization will not be renewed in the ordinary course. For the avoidance of doubt and notwithstanding the foregoing, neither the Company nor any subsidiary has applied for or holds any product licenses or marketing authorizations for any
pharmaceutical products. 
 4.11. United Kingdom FSMA and MAR. The Company has complied in all material respects with the U.K.
Financial Services and Markets Act 2000, as amended, and Regulation (EU) No 596/2014, in each case to the extent that they apply in relation to the subscription of Ordinary Shares and/or Warrants pursuant to this Agreement. 

4.12. Company SEC Documents; AIM Documents; Financial Statements; Nasdaq Stock Market. 

(a) Since February 1, 2019, the Company has timely filed all required reports, schedules, forms, statements and other documents (including
exhibits and all other information incorporated therein), and any required amendments to any of the foregoing, with the SEC (the “Company SEC Documents”). As of their respective filing dates, each of the Company SEC Documents
complied in all material respects with the requirements of the 1933 Act and the 1934 Act, and the rules and regulations of the SEC promulgated thereunder applicable to such Company SEC Documents, and no Company SEC Documents when filed, declared
effective or mailed, as applicable, contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in light of the circumstances under which
they were made, not misleading. 

  
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 (b) Since February 1, 2019, the Company has published documents required to be
published by it under the AIM Rules. Each of the AIM Documents was published within the applicable timeframe prescribed by the AIM Rules. As of their respective dates, each of the AIM Documents complied in all material respects with the applicable
requirements of the AIM Rules. 
 (c) As of the date of this Agreement, there are no outstanding or unresolved comments in comment letters
received from the SEC or its staff. 
 (d) The financial statements of the Company included in its Annual Report on Form 20-F for the fiscal year ended January 31, 2019 present fairly the financial position of the Company and its consolidated subsidiaries as of the dates indicated and the results of their operations and the
changes in their cash flows for the periods specified; such financial statements have been prepared in conformity with International Financial Reporting Standards as adopted by the European Union and the International Accounting Standards Board
(“IFRS”) applied on a consistent basis throughout the periods covered thereby, except as otherwise disclosed therein and, in the case of unaudited, interim financial statements, subject to normal
year-end audit adjustments and the exclusion of certain footnotes, and any supporting schedules included in the Company SEC Documents present fairly the information required to be stated therein. 

(e) The issued Ordinary Shares of the Company as of the date hereof are admitted to trading on AIM, a market operated by London Stock Exchange
plc (“AIM”). The Company intends to include a resolution (numbered four on the notice of general meeting that is appended to the Shareholder Circular) in the Shareholder Circular to approve the cancellation of trading of the
Ordinary Shares on AIM. The ADSs of the Company, representing Ordinary Shares, are listed on the Nasdaq, and the Company has taken no action designed to, or which is likely to have the effect of, terminating the registration of the Ordinary Shares
under the 1934 Act or delisting the ADSs from the Nasdaq. The Company has not received any notification that the SEC or the Nasdaq, as applicable, is contemplating terminating such registration or listing. 

(f) The Company and its subsidiaries have established systems of “internal control over financial reporting” (as defined in Rule 13a-15(f) of the 1934 Act) that have been designed by, or under the supervision of, their respective principal executive and principal financial officers, or persons performing similar functions, to provide
reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with IFRS, including, but not limited to, internal accounting controls sufficient to provide
reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with
IFRS and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing
assets at reasonable intervals and appropriate action is taken with respect to any differences. 
 (g) There is and has been no material
failure on the part of the Company or any of the Company’s directors or officers, in their capacities as such, to comply with any applicable provision of the Sarbanes-Oxley Act of 2002 and the rules and regulations promulgated in connection
therewith (the “Sarbanes-Oxley Act”), including Section 402 related to loans and Sections 302 and 906 related to certifications. 

  
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 4.13. Interim Financials. The published interim results of the Company and its
consolidated subsidiaries for the three months ended on April 30, 2019 and the three and six months ended July 31, 2019 have been prepared with all due care and attention (having regard to the fact that the results were made publicly
available) and on accounting bases and assumptions consistent with those adopted in the preparation of the audited financial statements of the Company and its consolidated subsidiaries for the financial year ended January 31, 2019 and the
corresponding interim results of the Company and its consolidated subsidiaries published in the immediately preceding financial year, except as otherwise disclosed therein. 

4.14. Absence of Certain Changes. Since the interim results of the Company and its consolidated subsidiaries for the three and six
months ended on July 31, 2019 were prepared: the businesses of the Company and its consolidated subsidiaries have been carried on in the ordinary and usual course; there has been no significant adverse change in the financial or trading
position of the Company taken as a whole or, to the best of the Company’s knowledge, information and belief, prospects of the Company; the Company has not acquired or disposed of or agreed to acquire or dispose of any of its assets or
businesses other than in the ordinary course of trading; the Company has not entered into any contract or commitment of an unusual, long-term and/or onerous nature or assumed any material liabilities (including contingent liabilities) (other than as
contemplated by the Transaction Documents); the Company has not paid or made any payment or transfer to shareholders of any dividend, bonus, loan or distribution other than to the directors of the Company in their capacity as such directors in a
manner consistent with the compensation of such directors as disclosed in the Company SEC Documents; and the Company has notified a Regulatory Information Service of all information required to be notified by it in accordance with the AIM Rules and
has complied in all respects with all the requirements of the AIM Rules applicable to the Company (including the disclosure and notification requirements) and any requests for disclosure made by the London Stock Exchange. 

4.15. Tax. All returns of each member of the Group for taxation purposes have been made for all periods up to and including
January 31, 2019, and all such returns are correct, and are not the subject of any dispute with or claim by HM Revenue & Customs or other relevant taxation authority (other than routine audits) which would be material to the Company
are not likely to result in any such dispute or claim. 
 4.16. Environmental. So far as the Company is aware, none of the Company nor
any member of the Group has any material obligation or liability with respect to pollution, hazardous substances or environmental matters and there are no circumstances which the Company considers are likely to give rise to the same. 

4.17. Insurance. The Company and each member of the Group maintain such insurance coverage against fire and other risks upon all their
assets and such public and employers’ liability as the directors of each such company consider appropriate, taking into account the nature and scale of their activities, the provisions of agreements binding upon it, such insurance is now in
force. The Company is not aware of any fact or matter which would lead to any such insurance being vitiated or repudiated, there is no material claim pending or outstanding and all premiums in respect of such insurances are duly paid. 

  
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 4.18. Intellectual Property. 

(a) Each member of the Group has (i) acted reasonably in seeking professional advice with regard to filing patent applications in respect
of material new inventions; (ii) adopted commercially reasonable and prudent practices with regard to the protection, prosecution and maintenance of its portfolio of patents, patent applications and trademarks and other material intellectual
property and the payment of renewal fees in respect thereof; (ii) adopted commercially reasonable and prudent practices to capture intellectual property rights in respect of material new inventions; and (iv) used commercially reasonable
practices to protect the confidentiality of all material non-patented know how. None of the intellectual property relating to the business of any member of the Group is the subject of any claim, opposition,
assertion, infringement, attack, right, action or other restriction or arrangement of whatsoever nature which does or may impinge upon the validity, enforceability or ownership of the same or the utilization thereof by any member of the Group to an
extent which is material in the context of the Group. So far as the Company is aware, and not having obtained freedom to operate opinions in respect of all of its intellectual property rights, none of the activities of any member of the Group
infringes in any material respect any right of any other person relating to intellectual property or gives rise to a material liability for any royalty or similar payment. 

(b) The intellectual property used or enjoyed by each member of the Group in connection with its business at the date of this Agreement, and
which is material to such business, is either legally and beneficially owned by that member of the Group, or licensed to, or used under the authority of the owner by, that member of the Group and are not subject to any mortgage, charge, lien or
other security interest in favor of any third party save as registered with the Registrar of Companies. 
 4.19. Offering. Subject to
the accuracy of the Investor’s representations set forth in Section 5, the offer, sale and issuance of the Purchased Securities (including the Warrant Shares) to be issued in conformity with the terms of this Agreement constitute
transactions which are exempt from the registration requirements of the 1933 Act and from all applicable state registration or qualification requirements. 

4.20. No Integration. The Company has not, directly or through any agent, sold, offered for sale, solicited offers to buy or otherwise
negotiated in respect of, any security (as defined in the 1933 Act), that is or will be integrated with the sale of the Purchased Securities or the Warrant Shares in a manner that would require registration of such securities under the 1933 Act.

 4.21. Brokers’ or Finders’ Fees. Except as arising pursuant to the Placing, neither the Company nor any of its
subsidiaries is a party to any contract, agreement or understanding with any person that would give rise to a valid claim against the Company or any of its subsidiaries for a brokerage commission, finder’s fee or like payment in connection with
the transactions contemplated by the Transaction Documents. 
 4.22. No General Solicitation. Neither the Company nor any person
acting on behalf of the Company has offered or sold any of the Purchased Securities by any form of general solicitation or general advertising. The Company has offered the Purchased Securities for sale only to the Investor. 

  
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 4.23. Foreign Corrupt Practices. None of the Company, any of its subsidiaries, nor to
the knowledge of the Company, any agent or other person acting on behalf of the Company or any of its subsidiaries, has: (i) directly or indirectly, used any funds for unlawful contributions, gifts, entertainment or other unlawful expenses
related to foreign or domestic political activity, (ii) made any unlawful payment to foreign or domestic government officials or employees or to any foreign or domestic political parties or campaigns from corporate funds, (iii) failed to
disclose fully any contribution made by the Company or any of its subsidiaries (or made by any person acting on its or their behalf of which the Company is aware) which is in violation of law or (iv) violated in any material respect any
provision of the Foreign Corrupt Practices Act of 1977, as amended, or any applicable non-U.S. anti-bribery Law. 

4.24. Regulation M Compliance. The Company has not taken, directly or indirectly, any action designed to or that would reasonably be
expected to cause or result in stabilization or manipulation of any of its securities to facilitate the sale or resale of the Purchased Securities. 

4.25. Investment Company. The Company is not required to be registered as, and is not an Affiliate of, and immediately following the
Closing will not be required to register as, an “investment company” within the meaning of the Investment Company Act of 1940, as amended. 

4.26. Shareholder Circular The Shareholder Circular has been prepared in accordance with all applicable laws and regulations, including,
but not limited to, the City Code. The Shareholder Circular is true and accurate in all material respects and contains all applicable information relevant to the matters referred to therein, except that the representations and warranties set forth
in this paragraph do not apply to statements or omissions in the Shareholder Circular based upon information relating to the Director Nominees furnished to the Company by such Director Nominees for use therein. 

4.27. Disclosures. The Company SEC Documents, when considered together, do not contain any untrue statement of a material fact or omit
to state a material fact necessary in order to make the statements contained therein, in light of the circumstances under which they were made, not misleading, other than with respect to the transactions contemplated by the Transaction Documents and
except as will be disclosed pursuant to Section 10.7.
 5. Representations and Warranties of the Investor. The Investor hereby
represents and warrants to the Company that: 
 5.1. Authority. The Investor is an individual with power and authority to enter into
and consummate the transactions contemplated by the Transaction Documents and to carry out its obligations thereunder, and to invest in the Purchased Securities pursuant to this Agreement. 

5.2. Authorization. This Agreement has been, and upon the execution and delivery of the Warrant Instrument, each such agreement will be,
duly executed and delivered by the Investor, and this Agreement constitutes, and upon execution and delivery of the Warrant Instrument, each such agreement will constitute, a valid and legally binding obligation of the Investor, enforceable against
the Investor in accordance with their respective terms, except as enforceability may be limited by the Enforceability Exceptions. 

  
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 5.3. No Conflicts. The execution, delivery and performance of this Agreement and the
Warrant Instrument and the consummation of the transactions contemplated by the Transaction Documents will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result
in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Investor pursuant to, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Investor is a party or by
which the Investor is bound or to which any of the property or assets of the Investor is subject, or (ii) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or
regulatory authority having jurisdiction over the Investor except, in the case of clauses (i) and (ii) above, for any such conflict, breach, violation or default that would not, individually or in the aggregate, have a material adverse effect
on the Investor’s ability to perform its obligations or consummate the transactions contemplated by the Transaction Documents. 
 5.4.
Purchase Entirely for Own Account. The Purchased Securities to be received by the Investor hereunder will be acquired for the Investor’s own account, not as nominee or agent, and not with a view to the resale or distribution of any part
thereof in violation of the 1933 Act, and the Investor has no present intention of selling, granting any participation in, or otherwise distributing the same in violation of the 1933 Act, without prejudice, however, to such Investor’s right at
all times to sell or otherwise dispose of all or any part of such Purchased Securities (including the Warrant Shares) in compliance with applicable federal and state securities laws. The Investor is not a broker-dealer registered with the SEC
under the 1934 Act or an entity engaged in a business that would require it to be so registered. 
 5.5. Investment Experience. The
Investor acknowledges that it can bear the economic risk and complete loss of its investment in the Purchased Securities and has such knowledge and experience in financial or business matters that it is capable of evaluating the merits and risks of
the investment contemplated hereby. 
 5.6. Disclosure of Information. The Investor has had an opportunity to receive, review and
understand all information related to the Company requested by it and to ask questions of and receive answers from the Company regarding the Company, its business and the terms and conditions of the offering of the Purchased Securities, and has
conducted and completed its own independent due diligence. The Investor acknowledges that copies of the Company SEC Documents are available on the SEC’s EDGAR system. Based on the information the Investor has deemed appropriate and the
representations and warranties of the Company contained in Section 4 of this Agreement, and without reliance upon any other party, it has independently made its own analysis and decision to enter into this Agreement. The Investor has sought
such accounting, legal and tax advice as it has considered necessary to make an informed investment decision with respect to its acquisition of the Purchased Securities. 

5.7. Restricted Securities. The Investor understands that the Purchased Securities are, and upon exercise of the Purchased Warrants in
accordance with their terms the Warrant Shares will be, characterized as “restricted securities” under the U.S. federal securities laws inasmuch as they are being or will be acquired from the Company in a transaction not involving a public
offering and that under such laws and applicable regulations such securities may be resold without registration under the 1933 Act only in certain limited circumstances. The Investor acknowledges that the Company has no obligation to register or
qualify the Purchased Securities or the Warrant Shares for resale. The Investor further acknowledges that if an exemption from registration or qualification is 

  
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available, it may be conditioned on various requirements including, but not limited to, the time and manner of sale, the holding period for the Purchased Securities and the Warrant Shares (which,
for the avoidance of doubt, will not begin with respect to the Warrant Shares until exercise of the Purchased Warrants in accordance with the terms of the Warrant Instrument, including the payment of any exercise price therefor), and on requirements
relating to the Company which are outside of the Investor’s control, and which the Company is under no obligation and may not be able to satisfy. 

5.8. Legends. It is understood that, except as provided below, certificates evidencing the Purchased Securities and the Warrant Shares
may bear the following or any similar legend: 
 (a) “The securities represented hereby have not been registered with the Securities and
Exchange Commission or the securities commission of any state in reliance upon an exemption from registration under the Securities Act of 1933, as amended, and, accordingly, may not be transferred unless (i) such securities have been registered
for sale pursuant to the Securities Act of 1933, as amended, (ii) such securities may be sold pursuant to Rule 144 or similar rule, or (iii) the Company has received an opinion of counsel reasonably satisfactory to it that such
transfer may lawfully be made without registration under the Securities Act of 1933, as amended.” 
 (b) If required by the authorities
of any state in connection with the issuance or sale of the Purchased Securities and the Warrant Shares, the legend required by such state authority. 

5.9. Accredited Investor. The Investor is (a) an “accredited investor” within the meaning of Rule 501 under the 1933 Act
and has executed and delivered to the Company a questionnaire in substantially the form attached hereto as Exhibit C (the “Investor Questionnaire”), which such Investor represents and warrants is true, correct and complete.
The Investor is (b) a sophisticated investor with sufficient knowledge and experience in investing in private equity transactions to properly evaluate the risks and merits of its purchase of the Purchased Securities. Such Investor has
determined based on its own independent review and such professional advice as it deems appropriate that its purchase of the Purchased Securities and participation in the transactions contemplated by the Transaction Documents (i) are fully
consistent with its financial needs, objectives and condition, (ii) comply and are fully consistent with all investment policies, guidelines and other restrictions applicable to such Investor, (iii) have been duly authorized and approved
by all necessary action, (iv) do not and will not violate or constitute a default under any law, rule, regulation, agreement or other obligation by which such Investor is bound and (v) are a fit, proper and suitable investment for such
Investor, notwithstanding the substantial risks inherent in investing in or holding the Purchased Securities. 
 5.10. No General
Solicitation. The Investor did not learn of the investment in the Purchased Securities as a result of any general solicitation or general advertising. 

5.11. Brokers and Finders. Except as arising pursuant to the Placing, no Person will have, as a result of the transactions contemplated
by the Transaction Documents, any valid right, interest or claim against or upon the Company or the Investor for any commission, fee or other compensation pursuant to any agreement, arrangement or understanding entered into by or on behalf of the
Investor. 

  
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 5.12. Short Sales and Confidentiality Prior to the Date Hereof. Other than
consummating the transactions contemplated hereunder, the Investor has not, nor has any Person acting on behalf of or pursuant to any understanding with the Investor, directly or indirectly executed any purchases or sales, including Short
Sales, of the securities of the Company or directly or indirectly engaged in any action designed to, or which might be reasonably expected to, cause or result in any manipulation of the price of the securities of the Company during the period
commencing as of the time that such Investor was first contacted by the Company or any other Person regarding the transactions contemplated hereby and ending immediately prior to the date hereof. The Investor has maintained the confidentiality
of all disclosures made to it in connection with this transaction (including the existence and terms of this transaction). Notwithstanding the foregoing, for avoidance of doubt, nothing contained herein shall constitute a representation or warranty,
or preclude any actions, with respect to the identification of the availability of, or securing of, available securities to borrow in order to effect Short Sales or similar transactions in the future. 

5.13. No Government Recommendation or Approval. The Investor understands that no United States federal or state agency, or similar
agency of any other country, has reviewed, approved, passed upon, or made any recommendation or endorsement of the Company or the purchase of the Purchased Securities. 

5.14. Shareholder Circular The Shareholder Circular is true and accurate in all material respects and contains all applicable
information relevant to the matters referred to therein, except that the representations and warranties set forth in this paragraph only apply to statements or omissions in the Shareholder Circular based upon information relating to the Director
Nominees furnished to the Company by such Director Nominees for use therein. 
 5.15. No Rule 506 Disqualifying Activities. The
Investor has not taken any of the actions set forth in, and is not subject to, the disqualification provisions of Rule 506(d)(1) of the 1933 Act. 

5.16. Offshore Resales. The Investor understands and is aware that Rule 904 of Regulation S under the 1933 Act regarding “Offshore
Resales” is not applicable to “affiliates” (as defined in Rule 405 under the 1933 Act) of the Company. 
 5.17. Acquiring
Person. As of the date of this Agreement and immediately prior to the Closing, neither the Investor nor any of its Affiliates beneficially owns, or will beneficially own (as determined pursuant to Rule
13d-3 under the 1934 Act without regard for the number of days in which a Person has the right to acquire such beneficial ownership, and without regard to Investor’s rights under this Agreement), any
securities of the Company, except (a) for securities that may be owned by employee benefit plans of the Investor or any of its Affiliates and (b) for 15,657,641 ADSs (representing 78,288,205 Ordinary Shares) which are owned by the Investor
and its Affiliates as of the date hereof. 
 5.18. Residency. The Investor is a resident of the jurisdiction set forth on Exhibit
A hereto. 
 5.19. Financial Assurances. As of the date of this Agreement and as of the Closing Date, the Investor has and will
have access to cash in an amount sufficient to pay to the Company the Aggregate Purchase Price. 

  
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 5.20. City Code. The Investor understands, is aware of and will comply with the
obligations of the City Code in connection with the transactions contemplated by the Transaction Documents. Without prejudice to the foregoing, the Investor shall not, and shall procure that any other person who is not an Independent Shareholder (as
such term is defined in the Shareholder Circular) shall not, vote on the resolution (numbered three on the notice of general meeting that is appended to the Shareholder Circular) to approve the waiver granted by the Panel on Takeovers and Mergers of
the obligations that would otherwise arise on the Investor to make a general offer to the shareholders of the Company pursuant to Rule 9 of the City Code. 

6. Conditions to Closing. 

6.1. Conditions to the Investor’s Obligations. The obligation of the Investor to purchase the Purchased Securities at
the Closing is subject to the fulfillment to the Investor’s satisfaction, on or prior to the Closing Date, of the following conditions, any of which (save for the attainment of Shareholder Approval and the attainment of Admission) may be waived
by the Investor with the agreement of the Company: 
 (a) The representations and warranties made by the Company in Section 4 hereof
shall be true and correct in all material respects as of the date hereof and on the Closing Date, except to the extent any such representation or warranty expressly speaks as of an earlier date, in which case such representation or warranty shall be
true and correct in all material respects as of such earlier date. The Company shall have performed in all material respects all obligations and covenants herein required to be performed by it on or prior to the Closing Date. 

(b) The Company shall have obtained any and all consents, permits, approvals (including the Shareholder Approval), registrations and waivers
necessary for consummation of the purchase and sale of the Purchased Securities and the consummation of the other transactions contemplated by the Transaction Documents, all of which shall be in full force and effect. 

(c) The Company shall have executed and delivered the Warrant Instrument. 

(d) The Company shall have executed and delivered the Deed of Termination. 

(e) No judgment, writ, order, injunction, award or decree of or by any court, or judge, justice or magistrate, including any bankruptcy court
or judge, or any order of or by any Governmental Authority, shall have been issued, and no action or proceeding shall have been instituted by any Governmental Authority, enjoining or preventing the consummation of the transactions contemplated by
the Transaction Documents. 
 (f) The Company shall have delivered a Certificate, executed on behalf of the Company by its Chief Executive
Officer or its Vice President, Finance, dated as of the Closing Date, certifying to the fulfillment of the conditions specified in subsections (a), (b), (d), (h) and (i) of this Section 6.1. 

  
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 (g) The Company shall have delivered a Certificate, executed on behalf of the Company by its
Secretary, dated as of the Closing Date, certifying the resolutions adopted by the Board of Directors of the Company approving the transactions contemplated by the Transaction Documents and the issuance of the Purchased Securities (including the
Warrant Shares), certifying the current versions of the articles of association of the Company and certifying as to the signatures and authority of persons signing this Agreement, the Warrant Instrument and related documents on behalf of the
Company. 
 (h) The Investor shall have received (i) an opinion from Wilmer Cutler Pickering Hale and Dorr LLP, the Company’s U.S.
counsel, dated as of the Closing Date, substantially to the effect set forth in Exhibit D hereto and (ii) an opinion from CMS Cameron McKenna Nabarro Olswang LLP, the Company’s U.K. counsel, dated as of the Closing Date,
substantially to the effect set forth in Exhibit E hereto. 
 (i) No stop order or suspension of trading shall have been imposed by
AIM or any governmental or regulatory body with respect to public trading in the Ordinary Shares. 
 (j) Admission shall have been attained,
and it shall have been attained no later than December 31, 2019, or such later date as the parties shall mutually agree in writing. 

(k) The Purchased Securities shall be delivered to the Investor. 

(l) The Resigning Directors shall have delivered to the Company executed resignation letters effective upon Admission. 

(m) The Company shall have delivered to the Director Nominees executed appointment letters effective upon Admission. 

6.2. Conditions to Obligations of the Company. The Company’s obligation to sell and issue the Purchased Securities at the Closing
is subject to the fulfillment to the satisfaction of the Company on or prior to the Closing Date of the following conditions, any of which (save for the attainment of Shareholder Approval and the attainment of Admission) may be waived by the Company
with the agreement of the Investor: 
 (a) The attainment of the Shareholder Approval. 

(b) The representations and warranties made by the Investor in Section 5 hereof shall be true and correct in all material respects as of
the date hereof, and shall be true and correct in all material respects on the Closing Date with the same force and effect as if they had been made on and as of said date. The Investor shall have performed in all material respects all obligations
and covenants herein required to be performed by it on or prior to the Closing Date. 
 (c) The Investor shall have executed and delivered
the Investor Questionnaire. 
 (d) The Investor shall have executed and delivered the Deed of Termination. 

(e) The Investor shall have paid in full the Aggregate Purchase Price to the Company. 

  
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 (f) Admission shall have been attained, and it shall have been attained no later than
December 31, 2019, or such later date as the parties shall mutually agree in writing. 
 6.3. Termination of Obligations to Effect
Closing; Effects. 
 (a) The obligations of the Company, on the one hand, and the Investor, on the other hand, to effect the Closing
shall terminate as follows: 
 (i) Upon the mutual written consent of the Company and the Investor; 

(ii) By the Company if any of the conditions set forth in Section 6.2 shall have become incapable of fulfillment, and shall not have been
(where capable of waiver) waived; 
 (iii) By the Investor if any of the conditions set forth in Section 6.1 shall have become
incapable of fulfillment, and shall not have been (where capable of waiver) waived; or 
 (iv) By either the Company or the Investor if the
Closing has not occurred on or prior to the day that is sixty (60) days following the date of this Agreement; 
 provided, however, that, except in the
case of clause (i) above, the party seeking to terminate its obligation to effect the Closing shall not then be in breach of any of its representations, warranties, covenants or agreements contained in this Agreement and the Warrant Instrument
if such breach has resulted in the circumstances giving rise to such party’s seeking to terminate its obligation to effect the Closing. 

(b) Nothing in this Section 6.3 shall be deemed to release any party from any liability for any breach by such party of the terms and
provisions of this Agreement or the Warrant Instrument or to impair the right of any party to compel specific performance by any other party of its obligations under such agreements. 

7. Covenants and Agreements of the Company. 

7.1. No Conflicting Agreements. The Company will not take any action, enter into any agreement or make any commitment that would
conflict or interfere in any material respect with the Company’s obligations to the Investor under this Agreement and, to the extent that the Investor continues to hold the Purchased Warrants, the Warrant Instrument. 

7.2. AIM Admission. The Company shall make or cause to be made an application to AIM for Admission. The Company shall use commercially
reasonable efforts to obtain Admission on or before the close of business on the third Business Day after receipt of the Shareholder Approval and will, at its own expense, use commercially reasonable efforts to supply or cause to be supplied all
such information, give all such undertakings, execute all such documents and take or cause to be taken all such action as may be required by AIM, in accordance with such application. 

  
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 7.3. Shareholders’ Meeting. The Company shall use commercially reasonable
efforts to, within thirty (30) days of the date hereof, convene and hold a meeting of shareholders for the purpose of obtaining the Shareholder Approval (the “Shareholders’ Meeting”). 

7.4. Shareholder Circular. The Investor consents to the use of its name in the Shareholder Circular in the form and context in which it
appears. The Company shall post the Shareholder Circular to its shareholders as soon as reasonably practicable after the date hereof, and the Company shall not delay or adjourn the Shareholders’ Meeting, except as required, in the reasonable
opinion of the Company, to obtain the Shareholder Approval. Any delay or adjournment of the Shareholders’ Meeting shall be undertaken in accordance with the articles of association of the Company. 

7.5. Removal of Legends. 

(a) In connection with any sale, assignment, transfer or other disposition of the Purchased Ordinary Shares or Warrant Shares by the Investor
pursuant to Rule 144 or pursuant to any other exemption under the 1933 Act such that the purchaser acquires freely tradable shares and upon compliance by the Investor with the requirements of this Agreement, if requested by the Investor, the
Company shall use commercially reasonable efforts to cause the Registrar to remove any restrictive legends that appear on the certificate that relates to the Purchased Ordinary Shares or Warrant Shares and to issue a new, unlegended certificate for
the Purchased Ordinary Shares or Warrant Shares sold or disposed of without restrictive legends, provided that the Company has received from the Investor customary representations and other documentation reasonably acceptable to the Company in
connection therewith and, if necessary, otherwise sufficient to support any required legal opinion with respect thereto. 
 (b) Subject to
receipt from the Investor by the Company and the Registrar of customary representations and other documentation reasonably acceptable to the Company and the Registrar in connection therewith and, if necessary, otherwise sufficient to support any
required legal opinion with respect thereto, upon the earliest of such time as the Purchased Ordinary Shares or Warrant Shares (i) have been sold or transferred pursuant to an effective registration statement, (ii) have been sold pursuant
to Rule 144, or (iii) are eligible for resale under Rule 144(b)(1) or any successor provision (such earliest date, the “Effective Date”), the Company shall (A) deliver to the Registrar irrevocable instructions that
the Registrar shall issue a new, unlegended certificate for such Ordinary Shares, and (B) cause its counsel to deliver to the Registrar one or more opinions to the effect that the removal of such legends in such circumstances may be effected
under the 1933 Act if required by the Registrar to effect the removal of the legend in accordance with the provisions of this Agreement. The Company agrees that following the Effective Date or at such time as such legend is no longer required under
this Section 7.5, it will, following the delivery by the Investor to the Company or the Registrar of a certificate representing Ordinary Shares issued with a restrictive legend, use commercially reasonable efforts to deliver or cause to be
delivered to such Investor a certificate representing such Ordinary Shares that is free from all restrictive and other legends. The Company may not make any notation on its records or give instructions to the Registrar that enlarge the restrictions
on transfer set forth in this Section 7.5. 
 (c) Subject to the restrictions on dispositions pursuant to Section 8.1 of this
agreement, the Investor agrees with the Company that the Investor will sell Purchased Ordinary Shares or Warrant Shares only in compliance with an exemption from the registration requirements of the 1933 Act. 

  
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 7.6. Subsequent Equity Sales. The Company shall not, and shall use its commercially
reasonable efforts to ensure that no Affiliate of the Company shall, sell, offer for sale or solicit offers to buy or otherwise negotiate in respect of any security (as defined in Section 2 of the 1933 Act) that will be integrated with the
offer or sale of the Purchased Securities in a manner that would require the registration under the 1933 Act of the sale of the Purchased Securities to the Investor, or that will be integrated with the offer or sale of the Purchased Securities for
purposes of the rules and regulations of any trading market such that it would require shareholder approval prior to the closing of such other transaction unless shareholder approval is obtained before the closing of such subsequent transaction.

 7.7. Short Sales and Confidentiality After the Date Hereof. The Investor covenants that neither it nor any Affiliates acting on its
behalf or pursuant to any understanding with it will execute any Short Sales during the period from the date hereof until the earlier of such time as (i) the transactions contemplated by this Agreement are first publicly announced or
(ii) this Agreement is terminated in full. The Investor covenants that until such time as the transactions contemplated by this Agreement are publicly disclosed by the Company, the Investor will maintain the confidentiality of all disclosures
made to it in connection with this transaction (including the existence and terms of this transaction). The Investor understands and acknowledges that the SEC currently takes the position that coverage of Short Sales of securities “against the
box” prior to effectiveness of a resale registration statement with securities included in such registration statement would be a violation of Section 5 of the 1933 Act, as set forth in Item 239.10 of the Securities Act Rules Compliance
and Disclosure Interpretations compiled by the Office of Chief Counsel, Division of Corporation Finance. 
 8. Insider Trading. In
addition to the restrictions in this Agreement on the Disposition of ADSs, Ordinary Shares and Ordinary Share Equivalents of the Company, the Investor hereby acknowledges that it is aware that the United States, the United Kingdom and other
applicable securities laws prohibit any person who has material, non-public information about a company obtained directly or indirectly from that company from purchasing or selling securities of such company
or from communicating such information to any other person, including under circumstances in which it is reasonably foreseeable that such person is likely to purchase or sell such securities. 

9. Survival. The representations, warranties, covenants and agreements contained in this Agreement shall survive the Closing of the
transactions contemplated by this Agreement for the applicable statute of limitations. 
 10. Miscellaneous. 

10.1. Successors and Assigns. This Agreement may not be assigned by a party hereto without the prior written consent of the Company or
the Investor, as applicable. The provisions of this Agreement shall inure to the benefit of and be binding upon the respective permitted successors and assigns of the parties. 

10.2. Counterparts; Faxes; E-mail. This Agreement may be executed in one or more counterparts,
each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed via facsimile or electronic mail, which shall be deemed an original. 

  
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 10.3. Titles and Subtitles. The titles and subtitles used in this Agreement are used
for convenience only and are not to be considered in construing or interpreting this Agreement. 
 10.4. Notices. Unless otherwise
provided, any notice required or permitted under this Agreement shall be given in writing and shall be deemed effectively given as hereinafter described (i) if given by personal delivery, then such notice shall be deemed given upon such
delivery, (ii) if given by facsimile or electronic mail, then such notice shall be deemed given upon receipt of confirmation of complete transmittal, (iii) if given by mail, then such notice shall be deemed given upon the earlier of
(A) receipt of such notice by the recipient or (B) three Business Days after such notice is deposited in first class mail, postage prepaid, and (iv) if given by an internationally recognized overnight air courier, then such notice
shall be deemed given one Business Day after delivery to such carrier. All notices shall be addressed to the party to be notified at the address as follows, or at such other address as such party may designate by ten days’ advance written
notice to the other party: 
 If to the Company: 

Summit Therapeutics plc 
 136a
Eastern Avenue 
 Milton Park, Abingdon, Oxfordshire 

OX14 4SB 
 Attention: Chief
Executive Officer 
 Fax: +44 (0)1235 443 999 

With a copy to: 
 Wilmer Cutler
Pickering Hale and Dorr LLP 
 7 World Trade Center 

250 Greenwich Street 
 New York,
New York 10007 
 Attention: Brian A. Johnson 

Fax: (212) 230-8888 

With a copy to: 
 CMS Cameron
McKenna Nabarro Olswang LLP 
 Cannon Place 

78 Cannon Street, London 
 EC4N
6AF, United Kingdom 
 Attention: Gary Green and James Parkes 

Fax: +44 (0)20 7367 2000 
 If to
the Investor: 
 to the address set forth on Exhibit A hereto. 

10.5. Expenses. The parties hereto shall pay their own costs and expenses in connection herewith regardless of whether the transactions
contemplated hereby are consummated; it being understood that each of the Company and the Investor has relied on the advice of its own respective counsel. 

  
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 10.6. Amendments and Waivers. Any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a particular instance and either retroactively or prospectively), only with the written consent of the Company and the Investor. 

10.7. Publicity. Except as set forth below, no public release or announcement concerning the transactions contemplated hereby shall be
issued by the Investor without the prior consent of the Company (which consent shall not be unreasonably withheld), except as such release or announcement may be required by law or the applicable rules or regulations of any securities exchange or
securities market, in which case the Investor shall allow the Company, to the extent reasonably practicable in the circumstances, reasonable time to comment on such release or announcement in advance of such issuance. The Company shall not include
the name of the Investor in any press release or public announcement (which, for the avoidance of doubt, shall not include any filing with the SEC) without the prior written consent of the Investor, except as otherwise required by law or the
applicable rules or regulations of any securities exchange or securities market, in which case the Company shall allow the Investor, to the extent reasonably practicable in the circumstances, reasonable time to comment on such release or
announcement in advance of such issuance. By 8:30 a.m. (New York City time) on the Business Day immediately following the date this Agreement is executed, the Company shall issue a press release disclosing all material terms of transactions
contemplated by this Agreement (the “Press Release”) and make an announcement thereof (including the name of the Investor) to a Regulatory Investment Service. No later than 5:30 p.m. (New York City time) on the fourth Business Day
following the date this Agreement is executed, the Company will file a Report on Form 6-K (the “6-K Filing”) attaching the press release described in
the foregoing sentence as well as copies of the Transaction Documents. In addition, the Company will make such other filings and notices in the manner and time required by the SEC, Nasdaq or AIM. The parties acknowledge that from and after the
issuance of the Press Release, the Investor shall not be in possession of any material, nonpublic information received from the Company or any of its respective officers, directors, employees or agents, with respect to the transactions contemplated
hereby that is not disclosed in the Press Release. 
 10.8. Severability. Any provision of this Agreement that is prohibited or
unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof but shall be interpreted as if it were written so as to be
enforceable to the maximum extent permitted by applicable law, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction. To the extent permitted by
applicable law, the parties hereby waive any provision of law which renders any provision hereof prohibited or unenforceable in any respect. 

10.9. Entire Agreement. This Agreement, including the signature pages and Exhibits hereto, constitutes the entire agreement among the
parties hereof with respect to the subject matter hereof and thereof and supersedes all prior agreements and understandings, both oral and written, between the parties with respect to the subject matter hereof and thereof, other than with respect to
the Securities Purchase Agreement, dated as of December 14, 2018, by and among the Company and the Investor, and the Nondisclosure Agreement, dated as of November 6, 2018, by and between the Company and the Investor, each of which shall
remain in full force and effect with respect to the subject matters thereof. 

  
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 10.10. Further Assurances. The parties shall execute and deliver all such further
instruments and documents and take all such other actions as may reasonably be required to carry out the transactions contemplated hereby and to evidence the fulfillment of the agreements herein contained. 

10.11. Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This Agreement shall be governed by, and construed in accordance
with, the internal laws of the State of New York without regard to the choice of law principles thereof. Each of the parties hereto irrevocably submits to the exclusive jurisdiction of the courts of the State of New York located in New York County
and the United States District Court for the Southern District of New York for the purpose of any suit, action, proceeding or judgment relating to or arising out of this Agreement and the transactions contemplated hereby. Service of process in
connection with any such suit, action or proceeding may be served on each party hereto anywhere in the world by the same methods as are specified for the giving of notices under this Agreement. Each of the parties hereto irrevocably consents to the
jurisdiction of any such court in any such suit, action or proceeding and to the laying of venue in such court. Each party hereto irrevocably waives any objection to the laying of venue of any such suit, action or proceeding brought in such courts
and irrevocably waives any claim that any such suit, action or proceeding brought in any such court has been brought in an inconvenient forum. EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT
TO THIS AGREEMENT AND REPRESENTS THAT COUNSEL HAS BEEN CONSULTED SPECIFICALLY AS TO THIS WAIVER. 
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blank] 

  
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 IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized
officers to execute this Agreement as of the date first above written. 
  

							
	COMPANY:	 		 	SUMMIT THERAPEUTICS PLC
				
		 		 	By:	 	 /s/ Glyn Edwards

		 		 		 	Name: Glyn Edwards
		 		 		 	Title: Chief Executive Officer














							
	INVESTOR:	 		 	
		 		 	By:	 	 /s/ Robert W. Duggan

		 		 		 	Name: Robert W. Duggan













 EXHIBIT A 

Investor 
  

			
	 Investor Information
	  	 
	Name:	  	Robert W. Duggan
		
	Contact Person:	  	
		
	Address:	  	
		
	City:	  	
		
	State:	  	
		
	Zip Code:	  	
		
	Telephone:	  	
		
	Facsimile:	  	
		
	Email:	  	
		
	Tax ID # or Social Security #:	  	
		
	Name in which Purchased Ordinary Shares, Purchased Warrants and Warrant Shares should be issued:	  	


  
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 EXHIBIT B 

Form of Warrant Instrument 

  
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 EXHIBIT C 

Investor Questionnaire 

  
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 EXHIBIT D 

Form of Opinion of Wilmer Cutler Pickering Hale and Dorr LLP 

  
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 EXHIBIT E 

Form of Opinion of CMS Cameron McKenna Nabarro Olswang LLP 

  
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 EXHIBIT F 

Shareholder Circular 

  
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