Ben Bernanke was on Thursday forced to make an unusual public defence of his actions as a bank regulator amid accusations he overstepped his authority during the frantic talks over Bank of America’s acquisition of Merrill Lynch.

Armed with hundreds of pages of subpoenaed e-mails, the House oversight committee asked the Federal Reserve chairman whether he and his staff forced BofA to go through with the deal, hid details from other regulators and threatened to fire Ken Lewis, chief executive of BofA, if he tried to pull out.