The FT reports that Tiner, who left the regulator in July 2007 to be replaced by Hector Sants, has backing from investors including Standard Life and RIT Capital, led by Lord Jacob Rothschild, and private equity firms Corsair and Centerbridge.
Under the deal Tiner would become chairman of the new firm with former Lloyds director and current Corsair chief executive John Maltby becoming chief executive.
The European Commission is forcing RBS to make the divestment after the bank’s 2008 bailout. The branches are believed to worth £1bn and include RBS branches in England and Wales with Natwest branches in Scotland.
Santander pulled out of a deal last year because of IT problems, leaving RBS without a buyer. RBS is now planning to float the business under the Williams & Glyn brand but says it is open to offers for the whole business.
Tiner’s deal is one of many offers being considered before the bid deadline this Thursday. RBS has until 2014 to secure a deal under EU rules and could seek an extension to the deadline if a sale is not imminent within a few months.