NASD, the US securities regulator, has hinted that US and European exchanges would have to abide by common rules following any transatlantic merger, contradicting earlier remarks by the Securities and Exchange Commission that common ownership would leave regulation untouched.

Robert Glauber, the chairman of the US National Association of Securities Dealers, yesterday said that without co-operation between national regulators the benefits of exchange consolidation will not be realised. He added that the American self-regulatory structure has a role to play in the integration of international regulation.