Pressure mounted on Michael Martin, the Commons Speaker, today after it emerged that his senior aide had quit claiming he was misled over taxpayer-funded shopping trips.

Some senior MPs have rallied around Mr Martin, saying he was the victim of a “witch-hunt” while others have called on the Speaker to hand over the inquiry into MPs’ expenses to an independent body.

Margaret Beckett, the former Foreign Secretary, told the BBC's Andrew Marr show, that there had been “a whole string of nasty stories” about the Speaker and added: “Clearly someone is out to get him. Whether any of it is valid, I can’t judge."

David Blunkett, the former Home Secretary, said he did not think Mr Martin should step down. Although he said he had not voted for him in the election for Speaker, he believed he had done a “pretty reasonable job” over the last seven years and said the stories about him amounted to a “witch-hunt”. MPs calling for the Speaker to resign should “stand up and be counted” Mr Blunkett told Sky News.

However Martin Bell, a former independent MP, said that MPs did not dare to speak out on the issue. “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,” Mr Bell told the BBC.

The row over Mr Martin’s expenses was intensified because of his position as chair of the review into MPs spending, set up after it was revealed that Tory MP Derek Conway paid his son £40,000 to work as a parliamentary researcher while he was a student at Newcastle University.

Sir Alistair Graham, the former sleaze watchdog, called on Mr Martin to hand over the entire investigation to an independent body.

“It’s unfortunate and really does undermine the credibility of this review that he himself has become part of this story, although it’s clear that he hasn’t broken any rules,” Sir Alistair told the BBC.

“But it does suggest the rules are inappropriate and need radically reforming.”

Sir Alistair said the Committee on Standards in Public Life, which he chaired until last year, should be given charge of the review currently being undertaken by the Commons Members Estimate Committee.

Lord George Foulkes, a leading Scottish Labour politician said the stories about Mr Martin were “a lot of unsubstantiated smear and innuendo” and part of a battle drawn out along class lines. He said that the campaign against Mr Martin was started years ago by “people who went to private schools and Oxbridge who didn’t like someone from a working class background in Glasgow getting into the highest office in the land”.

David Davis, the Shadow Home Secretary, was reluctant to comment on the future of Mr Martin, as a member of the front bench. However he told the Andrew Marr show: “Clearly he has got problems. The House of Commons needs to be much more transparent.”

Tony McNulty, Home Office minister agreed that greater transparency was necessary, but that allegations about MPs’ expenses were being thrown around “like confetti”.

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