A former Cabinet minister has raised concerns with Chancellor Philip Hammond that British financial institutions in South Africa could have been used as conduits for laundered money.
Ex-Northern Ireland secretary Lord Hain said it has been estimated that around £400 million could have been laundered through financial institutions in South Africa.
He said Mr Hammond had agreed that the matter would be looked into.
"I have written to the Chancellor asking for British authorities to investigate British financial institutions that may have been used as conduits for money laundering," Lord Hain said.
The Labour peer, who was a leading anti-apartheid campaigner, is set to raise the issue in the House of Lords on Thursday.
A Treasury spokesman said: "We take allegations of financial misconduct very seriously, and have passed Lord Hain's letter on to the Financial Conduct Authority and relevant UK law enforcement agencies, including the National Crime Agency and Serious Fraud Office, to agree the right action."
A spokeswoman for the Financial Conduct Authority said: "The FCA is already in contact with both banks named and will consider carefully further responses received."