The hearing of the House financial Services Committee covered numerous complex aspects of the sub-prime mortgage-based financial crisis, and the role played by complicated financial instruments.

Firms, large and small, can call upon all the external services needed to put together a complex financial deal, such as advice from lawyers and accountants, or the use of specialist markets.

Stock trading and other financial services would remain important to the combined company. But much of its income is expected to come from trading complex financial products called derivatives.