Ms Reeves is facing allegations by a whistleblower that she was investigated over her use of company money while working at Halifax Bank of Scotland (HBOS).
Lloyds, NatWest and Barclays made £30 billion between them last year by exploiting the gap between the rates for savers and borrowers, City experts say.
The announcement comes after Sir Keir and Ms Reeves on Tuesday told top City bosses including Lloyds chief executive Charlie Nunn that 'Britain is back and open for business'.