The bank, which has rebranded the high street branches of Abbey National, Alliance & Leicester and Bradford & Bingley, has called in the agency after holding talks with high profile consultancies, as revealed by PRWeek.
The news comes at a time when the UK Government is considering its next steps on banking regulation following the Barclays Libor scandal.
Labour leader Ed Miliband has called for a toughening of regulation, while economists have suggested that the Vickers report into banking reform does not go far enough.
It was widely expected the bank would hand the brief to Brunswick, which is rumoured to have been providing public affairs support on an interim basis as part of its ongoing brief to provide strategic comms and corporate advice.
A Santander UK spokesperson said: ‘Following a very competitive procurement process, Fleishman-Hillard has won the contract to become our new retained public affairs agency. This is the first time Santander UK has retained a public affairs agency since December 2011.’
PRWeek understands a pitch process was initially launched in late 2010, but this was put on hold when UK CEO Antonio Horta-Osorio left for Lloyds in December of that year, to be followed by comms director Matthew Young.
Santander formerly used Hanover until the agency resigned the account to take on Lloyds Banking Group in 2011.