The admission, made during mayor’s question time at the London assembly, has prompted a complaint to Richard Thomas, the information commissioner.

Livingstone had been challenged by Sally Hamwee, a Liberal Democrat member, over his office’s inadequate replies to requests for papers.

He responded by asking his opponents to be “more precise” if there is “anything particularly juicy you want to get your hands on”.

But he added: “There is almost nothing juicy in there; we never minute anything interesting. If there was, it was lost during shredding week just before January 1, 2005.”

The comments have outraged his political opponents. They claim he has failed to release key documents on subjects including fare increases and salaries paid to top advisers and consultants.

The Freedom of Information Act gives the public the right to see government documents that would not otherwise have been disclosed.From January 1 it became a criminal offence to destroy data if a valid request had been made under the act.

It is believed that many Whitehall departments and councils shredded sensitive documents before the new year. But Livingstone is believed to be the first political leader to be so brazen about it. The exchange, which took place at the end of February, has emerged as the result of a complaint made by the Lib Dems.

Graham Tope, leader of the Lib Dems in the assembly, has called on the information commissioner to ensure that the Labour mayor cannot hide behind “a wall of secrecy and silence”.

He said: “Some of the key decisions since Livingstone took office have cost London taxpayers hundreds of millions yet we have been told very little about them.

“It is deeply worrying that the mayor has shown such arrogant contempt for freedom of information laws.”

Livingstone’s opponents wish to look at his claims in his re-election campaign last year that there were unlikely to be above-inflation price rises in public transport, which is not now going to be the case. Opponents say he must have had meetings about the increases with Transport for London before the mayoral election last June.

The mayor’s office did not deny that the comments had been made. The Greater London Authority said: “The GLA takes its responsibilities under the Freedom of Information Act extremely seriously. It is incorrect to say little is known about the mayor’s policies and decisions.”

A spokesman for Thomas said that the complaint would be looked at closely.

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