British banks allowed two Nigerian politicians on corruption charges to deposit millions in illicit money overseas largely without questions, a report has claimed.
The watchdog group Global Witness blamed the banks for allowing former state governors Diepreye Alamieyeseigha and Joshua Dariye to funnel huge sums of money.
Its report called on Barclays, HSBC Holdings, NatWest, Royal Bank of Scotland and UBS to exercise stricter controls and closely monitor how much money foreign political leaders deposit into their accounts.
"Our financial system is morally complicit in Nigerian corruption," the report said.
"The Government must send a clear signal to the financial sector: Corrupt money is not welcome. And the banks themselves must demonstrate much more clearly the steps they are taking to stop dirty money entering the financial system."
HSBC said it had "rigorous and robust" measures in place to stop such abuses, but a spokesman said he could not discuss individual customers citing confidentiality.
Both Mr Alamieyeseigha and Mr Dariye's cases are examples of the culture of bribery that pervades life in Nigeria, where oil money funds nearly all government operations.
Government contracts often offer the nation's political elite a quick means to enrich themselves as more than 80% of people in Africa's most populous nation earn around £1.25 a day.
In one case, the report shows an employee at UBS "politely" asked Mr Alamieyeseigha about the millions of dollars coming into his account. The report said the then-governor of oil-rich Bayelsa state told the employee he expected more money to come into the account for a property sale, while he previously told the government he owned only a few hundred thousand dollars worth of land.
The employee accepted Mr Alamieyeseigha's answer, then tried to get him to set up an offshore trust fund - highlighting the pressure bank employees face in trying to close high value deals that involve politicians with questionable assets, the report said.