Ken Lewis, chief executive of Bank of America, used the threat of invoking a “material adverse change” clause to break off his agreement to buy Merrill Lynch last December because he wanted to negotiate a lower price, Federal Reserve chairman Ben Bernanke claimed in an e-mail.

Mr Lewis, who is scheduled to testify about the matter on Thursday at a congressional hearing, only dropped his threat after being told by former US Treasury secretary Hank Paulson that regulators, including Mr Bernanke, would remove him and his board if BofA tried to invoke the “MAC” clause.