Exhibit 12.1
  1.
    
    I have reviewed this annual report on Form 20-F of Santander UK plc;2.
    
    Based on my knowledge, this 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 report;3.
    
    Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material
respects the financial condition, results of operations and cash flows of the company as of, and for, the periods presented in this
report;4.
    
    The companys other certifying officer 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)) and internal control over financial reporting (as defined in Exchange Act Rules
13a-15(f) and 15d-15(f)) for the company 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 company, including its consolidated subsidiaries, is made
known to us by others within those entities, particularly during the period in which
this report is being prepared;(b)
    
    Designed such internal control over financial reporting, or caused such internal
control over financial reporting to be designed under our supervision, to provide
reasonable assurance regarding the reliability of financial reporting and the
preparation of financial statements for external purposes in accordance with generally
accepted accounting principles;(c)
    
    Evaluated the effectiveness of the companys disclosure controls and procedures and
presented in this report our conclusions about the effectiveness of the disclosure
controls and procedures, as of the end of the period covered by this report based on
such evaluation; and(d)
    
    Disclosed in this report any change in the companys internal control over financial
reporting that occurred during the period covered by the report, that has materially
affected, or is reasonably likely to materially affect, the companys internal control
over financial reporting; and
 5.
    
    The companys other certifying officer and I have disclosed, based on our most recent evaluation of
internal control over financial reporting, to the companys auditors and the audit committee of the
companys board of directors (or persons performing the 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 company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 companys internal control over financial reporting.
 Dated: 27 April 2010
    By:
    /s/ António Horta-OsórioAntónio Horta-OsórioChief Executive