I can imagine that there should be many people who have been put off by the rows that have been going on and feel that it is inappropriate

Lord Goodhart Liberal Democrat

Allegations that senior figures sabotaged Ms Filkin's inquiries have been dismissed by the Speaker and the Prime Minister Tony Blair.

But their denials have prompted Ms Filkin to issue a plea to MPs to step up efforts to root out Commons sleaze.

In comments to Thursday's Times newspaper, Ms Filkin said: "I'm saddened by the reaction because I hoped this would galvanise the House of Commons to sort these matters out in the future. That is the only thing I am seeking to do.

"The Commons should sit quietly for a moment and take stock on the lessons this teaches it about how it reacts to scrutiny."

Meanwhile, the Leader of the Commons Robin Cook called on Ms Filkin to back up her allegations about a "whispering campaign" against her.

'Damaged'

Ms Filkin decided not to re-apply for the job she has held since 1999, claiming it had been "downgraded" by MPs.

But despite her plea for better self-regulation, there are growing calls from the opposition for the role of Commons sleazebuster to be re-examined.

There are fears that the independence and status of the job has been irrevocably damaged, making it impossible to find a suitable replacement for Ms Filkin.

Liberal Democrat peer Lord Goodhart told BBC Radio 4's Today programme: "It is clearly something that will have been damaged.

"I can imagine that there should be many people who have been put off by the rows that have been going on and feel that it is inappropriate."

Lord Goodhart said the job should be re-examined by the independent Committee on Standards in Public Life, formerly known as the Nolan Commission, of which he is a member.

Among other things, it should examine whether the role of sleaze watchdog should be a full time one.

The committee should examine whether it - rather than MPs - should make the appointment and whether it should be a longer term non-renewable post, Lord Goodhart added.

'Whispering campaign'

Meanwhile, the Conservatives switched their focus to the role of the civil service, following Ms Filkin's suggestion that senior civil servants may have been involved in a "whispering campaign" against her.

Shadow cabinet office minister Tim Collins said Ms Filkin's allegations must be investigated in order to restore the reputation of the service.

Mr Collins also questioned the role of Downing Street and its communications chief Alastair Campbell.

"I suspect most people's off the top reaction will be that it is likely that if civil servants were involved they would have been politically appointed special advisors rather than career civil servants," he said.

However, Mr Collins said he suspected the row would strengthen the post in the long term.

"I think probably lessons have been learned and I suspect that the outcome of this will be a sufficient public backlash that the role will be bigger and more significant in the future than it would have been," he added.

Speaker hits back

Meanwhile, Commons Speaker Michael Martin has hit back at Ms Filkin's accusation that he had undermined her role.

Mr Martin said he was surprised Ms Filkin did not discuss her concerns about pressure from MPs with him at their regular meetings.

The watchdog's worries were unveiled in a letter she wrote to the speaker explaining how she believed her post had been "downgraded".

In a brief Commons statement, Mr Martin told MPs it was a matter of "great regret" to him that the letter had reached the media and said he was looking into how it happened.

The speaker said he was writing to ask Ms Filkin for more details about the "pressure" put on her as she investigated complaints against MPs.

High-profile figures

The role of standards commissioner was created in the aftermath of the 'sleaze' scandals of the early 1990s.

It involves checking complaints about the financial declarations and interests of MPs.

Peter Mandelson, Keith Vaz, Geoffrey Robinson, John Major and William Hague were among the high-profile figures to be investigated by Ms Filkin.