A joint opposition offensive intended to ensure Northern Rock cannot compete unfairly with other banks was launched at Westminster last night as the bill nationalising the lender started its breakneck passage through parliament. Financial Times

The Conservatives and Liberal Democrats fear Gordon Brown will allow the publicly owned bank to grab savings and mortgage business unfairly, increasing the value of the company when the government eventually sells it back to the private sector.

They hope to amend emergency legislation to nationalise Northern Rock when it arrives in the Lords today.

George Osborne, shadow chancellor, and Vincent Cable, Liberal Democrat Treasury spokesman, want the Office of Fair Trading to report annually on any distorting effects Northern Rock might have on the banking market.

Osborne was 'optimistic' the two parties could use their strong position in the upper house to amend the legislation, so that the OFT would report to parliament immediately it found any damage to banking competition.