The agency is understood to have been granted freedom to inject personality into brand campaigns for the bank's products such as First Active, Mint, NatWest and RBS.
The bank would only confirm that the agency is poised to carry out ‘a number of projects across the group'.
Neither party would provide further details.
Industry sources suggest fees are likely to be at least £200,000 a year. The hire follows an agency review (PRWeek, 23 June).