There are colleagues on all sides whom I respect who have thought that she was overstepping the mark

Tam Dalyell

He said members of all parties had complained of leaks to the media and investigations made on "frivolous, trivial and false grounds".

But Tory MP Peter Bottomley, a member of the MPs' committee which oversees Ms Filkin's work, defended her, saying the Labour government was "horrified" at her competence and what she had uncovered.

Impeding

Ms Filkin's highest profile scalp since she took office in 1998 was former Europe minister Keith Vaz - who was accused of impeding her investigatons into his business affairs.

The controversy is believed to have played a part in his removal from government although Mr Vaz insisted it was on health grounds.

She was also critical of John Major, Kenneth Clarke and Tory leader William Hague, who was accused of failing to declare that he used Lord Archer's private gym for judo practice.

The present Labour government are horrified by her competence and they would do anything to stop someone as good as her doing the job

Peter Bottomley

Senior MPs have been conducting a whispering campaign against Ms Filkin for some time, but Mr Dalyell spoke publicly on BBC Radio 4's Today programme on Thursday.

"There are colleagues on all sides whom I respect who have thought that she was overstepping the mark," said Mr Dalyell, Labour MP for Linlithgow.

"I wouldn't like anyone, whoever they are, to be re-appointed for another four year period."

Sullied

He added: "For an MP, her or his reputation is all important and if it's sullied it's difficult to de-sully it."

Mr Bottomley defended Ms Filkin, the former head of the Citizens Advice Bureaux, saying it would be a scandal if she was not re-appointed.

"The present Labour government are horrified by her competence and they would do anything to stop someone as good as her doing the job."

He said one of her problems was her lack of staff - she is only employed four days a week and has a staff of just four administrative assistants.

The decision on whether to re-appoint Ms Filkin will be made by the House of Commons commission, chaired by the Speaker, Michael Martin.

The BBC's political editor said Ms Filkin had suffered from the clash of cultures between the old system of behind-closed-doors investigation into MPs conduct and the new, quasi-judicial system set up with her post after Lord Nolan's inquiry into standards in public life.