The win includes the £5 million account for Cahoot, its internet banking arm.
TBWA already handles the Royal Bank of Scotland's The One account, formerly known as Virgin One, but both the agency and client are in discussions to resolve any potential conflict issues.
Luqman Arnold, the Abbey National chief executive, handled the high-speed review, which was completed in less than a week. He saw presentations from four undisclosed agencies.
"Euro RSCG worked with Abbey National for more than nine years, producing many creative and outstanding campaigns," Arnold said. "However, we now have a new management team, a new strategy and have taken the opportunity to take a fresh look in the market."
The TBWA chief executive, Andrew McGuinness, said: "This is the first major win for the new management team. To land a major client like this within six months of making management changes is great for the agency."
TBWA will work with its sister Omnicom agency Wolff Olins, which has been working on the bank's brand strategy since December.
During its almost decade-long tenure of the Abbey National account, Euro RSCG has survived five marketing directors. None of the original marketing team involved in the various hirings of Euro RSCG remain in their roles.
- Leader, p18.