Executives in the legal departments at Bank of America and Merrill Lynch were under strain on Thursday following revelations that the merger between the two banks was consummated only after BofA received a pledge of billions of dollars in support from the US government.

While BofA’s request for government aid undermined confidence in the North Carolina bank, driving the stock down 18 per cent to $8.32, the revelation raised legal questions concerning the disclosures made by both companies in the weeks leading up to January 1, when the deal formally closed.