Some of the world's biggest banks have been accused of dealing with some of the world's most corrupt regimes by Global Witness, the human rights and environmental campaign group.

Global Witness says that - in so doing - the banks, which include HSBC, Citigroup, Banco Santander and Barclays, allegedly have “facilitated” corruption and denied some of the world's poorest people the chance to escape poverty.

The report Undue Diligence, which is published today, has taken more than a year to prepare and has been released to coincide with this weekend's G20 summit of finance ministers in London. Among its allegations are claims that Barclays kept open an account for the son of the dictator of oil-rich Equatorial Guinea, despite evidence that his family had looted the country's oil revenues. It also accuses HSBC and Santander, Abbey's Spanish owner, of frustrating American efforts to investigate the looting and laundering of Equatorial Guinea's oil revenues by hiding behind bank secrecy laws in Luxembourg and Spain.

Global Witness, which was co-nominated for the 2003 Nobel Peace Prize for its work on conflict diamonds, accuses Citi of helping Charles Taylor, the warlord who is now on trial for war crimes in The Hague, to loot timber revenues in Sierra Leone and Liberia.

The report makes a number of recommendations on how money laundering laws should be tightened. It suggests that banks need to strengthen their due diligence into customers and says that governments must ensure that anti-money laundering laws are explicit and actively enforced.

It also called for more co-operation between governments to ensure that bank secrecy laws do not hinder anti-money-laundering measures - a call likely to win favour with many leading nations.

Gavin Hayman, Global Witness's campaigns director, said: “The same lax regulation that created the credit crunch has let some of the world's biggest banks facilitate the looting of natural resource wealth from poor countries.”

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