Pressure intensified on the Speaker of the Commons, Michael Martin, after a former standards watchdog warned that controversy over his expenses had undermined the credibility of his "root and branch" review of parliamentary allowances.
Sir Alistair Graham, the former chairman of the Committee on Standards in Public Life, said Mr Martin should hand over the inquiry to an independent body. His comments follow reports about the Speaker's allowances for his Scottish home and controversy about £4,000 claimed for taxi journeys taken by his wife, Mary.
On Saturday, Mr Martin's official spokesman, the former Whitehall communications chief Mike Granatt, resigned for "ethical" reasons after admitting he had been led to give wrong information to journalists about Mrs Martin's taxi trips. He had initially said that Mrs Martin was accompanied on the journeys by a Commons official, but quit after learning that she made the trips with a housekeeper.
Yesterday the Taxpayers' Alliance entered the row, asking the Parliamentary Commissioner for Standards, John Lyon, to investigate the £4,000 transport claims. Reports also highlighted Mr Martin's claim of more than £17,000 last year to cover costs at his Glasgow home. Senior ministers and backbenchers lined up to support Mr Martin, insisting he was the victim of a "witch hunt". The former foreign secretary Margaret Beckett said: "There have been a whole string of nasty stories around Michael Martin. Clearly someone is out to get him. Whether any of it is valid, I can't judge."
But the row intensified pressure on Mr Martin, who is chairing the Commons internal review into members' allowances that was set up in the wake of the Derek Conway affair. Last week he also faced criticism for using air miles earned on official business to help pay for flights for family members.
Sir Alistair told the BBC: "What the latest story ... does suggest is that his review of MPs' expenses and allowances really cannot have any credibility now. I was strongly opposed to members of Parliament reviewing their own arrangements.
"I thought the only way it could have any credibility is to be done by a body outside of Parliament. The fact that the Speaker has become the story makes this even more urgent."
Martin Bell, the journalist and former independent MP, said: "We've reached a point where the inquiry into expenses and allowances is going to be conducted by members of the old guard under the chairmanship of the Speaker so we are in a very difficult situation. He is not the victim of a witch hunt. He is protected by a wall of silence, actually, because MPs can talk about anything they like, inside or outside the House, except their views about the Speaker. They do not speak up and we know there is widespread disquiet on both sides of the House and no one dare speak up."
Mark Wallace, campaign director of the Taxpayers' Alliance, said: "The public are extremely concerned that some politicians may be taking advantage of the money provided to them to support the democratic process."
David Davis, the shadow Home Secretary, told BBC1's The Andrew Marr Show: "Clearly he has got problems. The House of Commons needs to be much more transparent." One senior MP said: "The general view is that he should stand down. He has had a long innings and he has not done particularly well. But I don't think he will unless Gordon Brown, David Cameron and Nick Clegg tell him to."
Privately Labour MPs expressed fury at the attacks on Mr Martin. One said: "It's a disgraceful, vindictive and co-ordinated campaign against him. It's bang out order." Andrew Dismore, a Labour member of the Committee on Standards and Privileges, added: "We are seeing a witch hunt against Michael Martin. There are some people who have never accepted that a former metal worker and trade unionist should be Speaker."
The Speaker's office would not comment on the row.
The aide who quit
Since his early days as a crisis-management expert, Mike Granatt's motto has been "believe it will happen". Now that it has, he will need his slick PR skills more than ever.
Mr Granatt, one of the most experienced PR figures in Whitehall, established the Cabinet Office secretariat to deal with civil emergencies.
He became the most senior figure in the civil service press machine and in 2001 was named among the 10 most important figures in PR.
"In PR, you get involved with the most interesting issues anywhere and everywhere. It's the most fun you can have with your clothes on," he was quoted as saying.
Mr Granatt has been press secretary to five cabinet ministers, and has been responsible for PR at the energy and environment departments, the Home Office and the Metropolitan Police Service. Crises from the millennium bug to the fuel tax protests of 2000 have found their way into his in-tray. He played a significant role in the row over "burying bad news" which cost the cabinet minister Stephen Byers his job.
After leaving the public sector to join the PR agency Luther Pendragon, Mr Granatt was hired in 2004 to speak for the House of Commons commission and improve the image of the Speaker, Michael Martin.
In 2001 he was appointed a Companion of the Bath for exceptional public service.