The bank is still looking into allegations that small firms were pushed into the Global Restructuring Group (GRG) in order for RBS to charge higher fees and interest and take control of their assets.

A source told the Reuters news agency that RBS’s board of directors has now invited outsiders to investigate alongside the Financial Conduct Authority (FCA) and identify any inconsistencies with their findings.

Bank insiders have called the allegations “reputationally damaging”, prompting renewed efforts to build trust with business customers.

A senior source at the bank said they wanted to improve their reputation before the UK government makes good on its commitment to sell at least 58 per cent of the bank - of which it owns 78 per cent - back to the private sector.

RBS previously commissioned law firm Clifford Chance to conduct a review into the GRG, which found no evidence that the bank set out to defraud SMEs.

However, the latest investigation will reportedly be more far-reaching.

The FCA has hired consultancy Promontory Financial Group and accounting firm Mazars to conduct its review, which will be published at the end of the year.