~~Page 1 of 4~~ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 6-K Report of Foreign Private Issuer Pursuant to Rule 13a-16 or 15d-16 under the Securities Exchange Act of 1934 For the month of ~~October~~January, ~~2025~~2026 Commission File Number 001-14928 SANTANDER UK PLC (Translation of registrant's name into English) 2 Triton Square, Regent's Place, London NW1 3AN, England (Address of principal executive office) Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F. Form 20-F . . . .X. . . . Form 40-F . . . . . . . .

~~Page 2 of 4 3 October 2025~~ Santander UK ~~Group~~- ~~Holdings~~Appointment ~~plc~~of ~~and~~new ~~Santander~~Chief UKExecutive ~~plc~~Officer The ~~(together~~Boards "of Santander UK") ~~announce~~announced ~~Mike Regnier to step down as Santander UK CEO Santander UK~~ today, ~~announced~~30 ~~that~~January ~~Chief Executive~~2026, ~~Mike~~the ~~Regnier,~~appointment ~~has~~of ~~confirmed~~Mahesh ~~his~~Aditya ~~intention to step down~~ as UKChief ~~CEO~~Executive byOfficer Q1of ~~2026. Mike joined~~ Santander UK inGroup ~~March~~Holdings ~~2022~~plc and heSantander ~~has~~UK ~~overseen~~plc awith ~~significant~~effect ~~programme~~from of1 ~~change~~March ~~and~~2026. Mahesh ~~transformation~~joins ~~within the business, culminating in the acquisition of TSB Banking Group plc~~ from Banco ~~Sabadell~~Santander, ~~subject~~where tohe ~~regulatory~~has ~~approval,~~been ~~in July~~Group ofChief ~~this~~Risk ~~year. An~~Officer ~~appointment~~since ~~process~~2023 toand ~~find~~prior ~~Mike’s successor has started. Mike Regnier said: "It is my intention~~ to ~~step~~that ~~down~~spent assix ~~CEO of Santander UK by Q1 2026 after what will be four~~ years ~~of great~~ ~~strategic~~at ~~success~~Santander ~~for~~in the ~~business~~US, ~~culminating in the decision by the Group earlier this year to acquire TSB to accelerate our transformation. “It had been my intention to move on after 4-5 years with Santander~~ as IChief ~~have~~Risk ~~other interests I would like to pursue. Given that the integration of TSB will take considerably longer than this~~Officer, ISantander ~~have~~US ~~suggested~~for totwo ~~the Board that now would be a good time to find a successor who can see this critical project through to its completion and beyond. “The integration will take time and focus~~years, ~~alongside~~followed ~~the~~by ~~ongoing~~CEO ~~transformation~~ of Santander UKConsumer ~~which~~USA ~~has strong momentum~~from ~~under~~2019 ~~an excellent Board and management team. Judging the right moment~~ to ~~move on is very important to ensure leadership stability through a period of intense change and opportunity~~2023. ~~The~~  He ~~foundations~~has ~~are~~over in30 ~~place~~years’ tofinancial ~~create~~services ~~the~~experience ~~best~~having ~~bank~~held ~~for customers~~positions inacross ~~the UK, fully integrated into the global banking group that is Santander. What was once~~ a ~~group~~range of ~~banks~~blue-chip isbrands ~~becoming~~including ~~a truly important banking group~~Citi, ~~for~~JPMorgan ~~the~~Chase ~~benefit~~& ofCo ~~customers, shareholders, employees~~ and ~~the~~Capital ~~economies we serve~~One. ~~“The~~  Mahesh ~~process~~was toappointed ~~find my successor is underway and I look forward~~ to ~~welcoming and handing over to them in due course so~~ the ~~momentum can continue." Ana Botin, Executive Chair of Banco~~ Santander, ~~said "Mike has done an excellent job in his four years with Santander. We now have real momentum in the transformation of the~~ UK ~~bank,~~Boards leveraging the investment and scale of the Group in its strategy to become the best bank for customers in the UK and for our shareholders. Our decision to acquire TSB accelerates our strategy and is a clear statement of intent in our ambition for (Santander ~~in the~~ UK. ~~Mike~~Group ~~was~~Holdings ~~always~~plc ~~very clear about his intention to stay for up to 5 years. His decision allows an orderly transition~~ and stable leadership through a very important integration project and the creation and growth of the newly enhanced bank. I am very grateful to Mike and wish him every success in what he does next." Tom Scholar, Chair Santander UK, ~~said:~~plc) ~~“The~~on ~~Board~~1 isOctober ~~very grateful to Mike for his leadership and drive over the last four years~~2025. He has maintained a strong team culture and cohesion through a period of significant change which is a testament to his abilities as a leader. With strong succession plans in place, we expect to be able to conclude the process to appoint a successor in the early part of 2026.” - Ends –- ~~For media enquiries, please contact: Stewart Todd Head of Communications mediarelations@santander.co.uk~~ Additional information about Santander UK ~~and Banco Santander~~ Santander UK is a financial services provider in the UK that offers a wide range of personal and commercial financial products and services. The bank serves its customers via a nationwide branch network, telephone, mobile and online banking. Santander UK is subject to the full supervision of the FCA and the PRA in the UK. Santander UK plc customers'’ eligible deposits are protected by the FSCS in the UK. ~~Banco Santander (SAN SM, STD US, BNC.LN) is a leading commercial bank, founded in 1857 and headquartered in Spain and~~

~~Page~~SIGNATURES Pursuant 3to ofthe ~~4 one~~requirements of the ~~largest~~Securities ~~banks~~Exchange inAct ~~the~~of ~~world by market capitalisation. The group's activities are consolidated into five global businesses: Retail & Commercial Banking~~1934, ~~Digital Consumer Bank, Corporate & Investment Banking (CIB), Wealth Management & Insurance and Payments (PagoNxt and Cards). This operating model allows~~ the ~~bank~~registrant tohas ~~better~~duly ~~leverage~~caused ~~its~~this ~~unique~~report ~~combination of global scale and local leadership. Banco Santander aims~~ to be ~~the~~signed ~~best~~on ~~open~~its ~~financial~~behalf ~~services platform providing services to~~by ~~individuals,~~the ~~SMEs~~undersigned, ~~corporates,~~thereunto ~~financial~~duly ~~institutions~~authorized. SANTANDER ~~and~~UK ~~governments.~~PLC By: ~~The~~/ ~~bank'~~s ~~purpose~~/ isRoz toRule Roz ~~help~~Rule Company ~~people and businesses~~Secretary ~~prosper~~Dated: in30 ~~a simple~~January, ~~personal and fair way. Banco Santander has a listing of its ordinary shares on the London Stock Exchange and Santander UK plc has preference shares listed on the London Stock Exchange.~~ 2026

Page 4 of 4 SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized. SANTANDER UK PLC By: / s / Roz Rule Name: Roz Rule Title: Company Secretary Dated: October 3, 2025

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