The joint offer from the firms has been rejected by RBS according to Sky News, which said other buyers including Anacap Financial had also been brushed off.
Virgin Money, which has the backing of buyout firm WL Ross, is thought to have stopped working on an offer but could still be interested in theory, the report added.
The bank tried to sell the branches to Santander last year, but the deal fell apart in October after the Spanish banking group walked away amid concerns the deal would not be completed until 2014.
The FT has previously said the sale was now likely to struggle to hit £1bn, as the £1.65bn agreement with Santander in 2010 took place in a better environment for UK and SME retail lending.
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