RBS is one of 13 banks facing a heavy fine after being charged by regulators with collusion to use anti-competitive practices.

The Edinburgh-based bank could be fined up to 10% of its global turnover if found guilty of flouting EU regulations by excluding rivals from the lucrative trading of credit derivatives.

The European Commission said it had issued a complaint against the firms, which include Barclays, HSBC, Citigroup, Deutsche Bank and UBS, after finding evidence they blocked two exchanges from full trading in credit default swaps, a form of insurance that pays out when a company or country fails to honour a debt. The commission said the banks acted collectively to shut out exchanges from the market because they feared the credit derivatives trading would have cut their own revenues from acting as intermediaries in the over-the-counter market.

The EU also charged Markit as well as the International Swaps and Derivatives Association, the banks' trade body, with aiding the anti-competitive practices.

The commission alleges that when the exchanges turned to ISDA and Markit to obtain necessary licences for data and index benchmarks the banks instructed them to license only for "over-the-counter" trading purposes.

RBS declined to comment.