A study by Global Witness, an anti-corruption monitoring body, revealed that despite previous warnings from the Financial Services Authority (FSA), banks have continued to take illegally-obtained money from Nigerian governors.
RBS was found to have allowed Dieypreye Alamieyeseigha, a former politician in the state, to bring an estimated Â£2.7 million into the UK.
The report, which examined court documents from London, showed that Â£1.56 million of this figure came in the form of bribes paid by a contractor to win work.
Robert Palmer, campaigner at Global Witness, said: âBanks are quick to penalise ordinary customers for minor infractions but seem to be less concerned about dirty money passing through their accounts.
âLarge scale corruption is simply not possible without a bank willing to process payments from dodgy sources, or hold accounts for corrupt politicians.â
HSBCâs North American unit was recently requested to improve its due diligence systems by US regulators.
The Federal Reserve made the request to ensure that the bankâs division adhered to regulations surrounding the Bank Secrecy Act and Anti-Money Laundering rules.
By Jim Ottewill