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                                                                    Exhibit 31.1

                                 PROTHERICS PLC

                            CERTIFICATION PURSUANT TO
           RULE 13a-14(a) UNDER THE SECURITIES ACT OF 1935, AS AMENDED
      AS ADOPTED PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, Andrew J. Heath, certify that:

      1.    I have reviewed this annual report on Form 20-F of the registrant,
Protherics PLC;

      2.    Based on my knowledge, this annual report does not contain any
untrue statement of a material fact or omit to state a material fact necessary
to make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by this
annual report;

      3.    Based on my knowledge, the financial statements, and other financial
information included in this annual report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
registrant as of, and for, the periods presented in this annual report;

      4.    The registrant's other certifying officer(s) and I are responsible
for establishing and maintaining disclosure controls and procedures (as defined
in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

            a)    designed such disclosure controls and procedures, or caused
      such disclosure controls and procedures to be designed under our
      supervision, to ensure that material information relating to the
      registrant, including its consolidated subsidiaries, is made known to us
      by others within those entities, particularly during the period in which
      this annual report is being prepared;

            b)    evaluated the effectiveness of the registrant's disclosure
      controls and procedures and presented in this annual report our
      conclusions about the effectiveness of the disclosure controls and
      procedures, as of the end of the period covered by this annual report
      based on such evaluation; and

            c)    disclosed in this annual report any change in the registrant's
      internal control over financial reporting that occurred during the
      registrant's most recent fiscal quarter (the registrant's fourth fiscal
      quarter in the case of an annual report) that has materially affected, or
      is reasonably likely to materially affect, the registrant's internal
      control over financial reporting; and

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      5.    The registrant's other certifying officer(s) and I have disclosed,
based on our most recent evaluation of internal control over financial
reporting, to the registrant's auditors and the audit committee of the
registrant's board of directors (or persons performing equivalent functions):

            a)    all significant deficiencies and material weaknesses in the
      design or operation of internal control over financial reporting which are
      reasonably likely to adversely affect the registrant's ability to record,
      process, summarize and report financial information; and

            b)    any fraud, whether or not material, that involves management
      or other employees who have a significant role in the registrant's
      internal control over financial reporting.

Date: July 22, 2005

                                                      /s/ Andrew J. Heath
                                                      --------------------------
                                                      Andrew J. Heath
                                                      Chief Executive Officer