Lloyds Banking Group has called in Hanover as its retained public affairs adviser after a keenly fought pitch process.
The part-nationalised bank will switch to Charles Lewington's agency after just 18 months with College Public Policy. Hanover has resigned its account with rival bank Santander in order to focus on the new brief.
Lewington said: 'We are sorry to be leaving Santander, but the chance to work for Britain's biggest bank in the current regulatory climate was irresistible.'
Lloyds, which is 40 per cent owned by the British Government after a bailout during the 2008 credit crisis, shocked investors this month with news that its chief executive Antonio Horta-Osorio was taking a break due to stress-related illness, leaving a potential power vacuum.
Given the upheaval, investors have said they are unclear over who will lead Lloyds in 2012, when it faces major challenges from increased regulation, the economic downturn and plans to sell off 630 retail branches and cut 15,000 jobs.
Hanover is expected to report to Dominic Morris, director of public policy and regulation. Morris, a former private secretary to John Major, joined the banking group in 2009 from Digital Britain.
The win is a boost for Hanover, which has made a concerted effort to reel in major clients in the financial services sector. It currently has retained public affairs accounts with corporate heavyweights such as Goldman Sachs, Nomura and the Association of British Insurers.
After a long-running pitch process, Hanover is believed to have triumphed in a final three-way shoot-out, with Burson-Marsteller narrowly missing out.
Hanover takes over from College Public Policy, which took the Lloyds business from Citigate Dewe Rogerson in July 2010. College's work is understood to have focused on political monitoring and intelligence-gathering, but the brief may have since increased in scope - Lewington insisted that Hanover's account was wide-ranging.
Lewington declined to comment on the value of the brief, but it is understood the account is worth significantly more than £100,000 a year in fees. The account will be led by Lewington and director Laura Chisholm.