SANTANDER UK PLC

Prospectus • Sep 2, 2025

SUPPLEMENT DATED 29 AUGUST 2025 TO THE BASE PROSPECTUS DATED 1 OCTOBER 2024

Santander UK plc

(incorporated in England and Wales with limited liability, registered number 2294747)

This supplement (the "Supplement") is prepared as a supplement to, and must be read in conjunction with the Base Prospectus dated 1 October 2024, as supplemented by the supplements dated 20 November 2024 and 10 March 2025, relating to the Issuer's programme for the issuance of Notes and Certificates (the "Base Prospectus").

This Supplement together with the Base Prospectus constitutes a base prospectus for the purposes of Article 8 of Regulation (EU) 2017/1129 as it forms part of UK domestic law by virtue of the European Union (Withdrawal) Act 2018 (as amended, the "EUWA") and regulations made thereunder (as amended, the "UK Prospectus Regulation"). Terms defined in the Base Prospectus have the same meaning when used in this Supplement.

This Supplement has been approved as a supplementary prospectus by the Financial Conduct Authority ("FCA") as competent authority under the UK Prospectus Regulation. The FCA only approves this Supplement as meeting the standards of completeness, comprehensibility and consistency imposed by the UK Prospectus Regulation. Such approval relates only to the Securities which are to be admitted to trading on a UK regulated market for the purposes of Directive 2014/65/EU, as amended as it forms part of UK domestic law by virtue of the EUWA (as amended, the "UK Markets in Financial Instruments Directive") or which are to be offered to the public in the United Kingdom and should not be considered as an endorsement of the Issuer or the N&C Securities that are the subject of this Supplement. Investors should make their own assessment as to the suitability of investing in the N&C Securities.

The Issuer accepts responsibility for the information contained in this Supplement. To the best of the knowledge of the Issuer, the information contained in this Supplement is in accordance with the facts and does not omit anything likely to affect the import of such information.

This Supplement has been prepared for the purpose of incorporating by reference the unaudited half yearly financial report of the Issuer for the six months ended 30 June 2025 (as described in Schedule 1 hereto).

To the extent that there is any inconsistency between (a) any statement in this Supplement or any statement incorporated by reference in the Base Prospectus by this Supplement and (b) any other statement in or incorporated by reference in the Base Prospectus prior to the date of this Supplement, the statement referred to in (a) above will prevail.

If any documents which are incorporated by reference themselves incorporate any information or other documents therein, either expressly or implicitly, such information or other documents will not form part of this Supplement or the Base Prospectus for the purposes of the UK Prospectus Regulation except where such information or other documents are specifically incorporated by reference or attached to this Supplement.

Any non-incorporated parts of a document referred to herein are either deemed not relevant for an investor or are otherwise covered elsewhere in the Base Prospectus, to which this Supplement relates.

Save as disclosed in this Supplement, no significant new factor, material mistake or inaccuracy relating to information included in the Base Prospectus has arisen or been noted, as the case may be, since the publication of the Base Prospectus.

In accordance with Article 23(2) of the UK Prospectus Regulation and Rule 3.4.1 of the UK Prospectus Regulation Rules, investors who have agreed to purchase or subscribe for securities before this Supplement is published have the right, exercisable before the end of the period of two working days beginning with the working day after the date on which this Supplement was published, to withdraw their acceptances by sending a written notice of withdrawal (which must include the full name and address of the person or entity wishing to exercise such statutory withdrawal right and identify the transferable securities to which that statutory withdrawal right relates) by electronic mail to structurednotesafm@santander.co.uk. The final date for any such withdrawal is 2 September 2025.

SCHEDULE 1

DOCUMENTS INCORPORATED BY REFERENCE

The Issuer has published its unaudited half yearly financial report for the six months ended 30 June 2025 (the "2025 Half Yearly Report").

The 2024 Half Yearly Report is hereby incorporated in and forms part of the Base Prospectus and is available viewing at:

https://www.santander.co.uk/assets/s3fspublic/documents/Santander%20UK%20plc%202025%20Half%20Yearly%20Financial%20Report.pdf.