Speaker of the House of Commons Michael Martin is facing increasing pressure after a newspaper published details of allowance claims for his Scottish home.
Michael Martin chairs the committee which oversees MPs' expenses
The Sunday Times story comes after Mr Martin's spokesman quit over issuing wrong information about expenses.
Former foreign secretary Margaret Beckett said someone was "out to get" him by telling "nasty little stories".
Ex-sleaze watchdog Sir Alistair Graham urged Mr Martin to hand his review of MPs' expenses to an independent body.
The Speaker, as chairman of the Commons Members Estimates Committee, is heading a "root and branch" parliamentary inquiry into all aspects of MPs' expenses.
This was set up after revelations that Tory MP Derek Conway had made payments worth £40,000 to his son for work as a parliamentary researcher while he was a student at Newcastle University.
Mr Conway has lost the Conservative Party whip and is to stand down as an MP at the next general election.
But Sir Alistair, former chairman of the Committee for Standards in Public Life, told the BBC: "It's unfortunate and really does undermine the credibility of this review that he [Mr Martin] himself has become part of this story, although it's clear that he hasn't broken any rules.
"But it does suggest the rules are inappropriate and need radically reforming."
He added: "The rules are wrong in my view. There clearly is scope for abuse on things like the housing allowance...
"The scope for reform is pretty enormous, but unfortunately now the Speaker and the committee the Speaker chairs is not the body to carry out that reform."
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A number of MPs are said to want Mr Martin to step down, as Parliament's standards watchdog probes a complaint over his alleged use of air miles.
Mr Martin, MP for Glasgow North East, has been accused of flying members of his family in business class from Glasgow to London for a New Year break, using air miles gained from official trips.
And the Sunday Times is among newspapers reporting he has claimed £17,000 a year for his home in Scotland and £7,500 in costs for using that home as an office.
But BBC political correspondent Ben Wright said these figures had been publicly declared already and there was no suggestion Mr Martin had not used his allowance correctly.
The resignation of Mr Martin's spokesman, Mike Granatt, came after he rebutted a story that Mr Martin's wife had claimed more than £4,000 in taxpayer-funded taxi expenses since May 2004.
He said any shopping trips she had undertaken had been for food for government-related functions, and Mrs Martin had been accompanied by an official at all times.
But Mr Granatt later learned that the official was actually a housekeeper from the Speaker's household.
He was adamant that Mr Martin was not at fault over the misinformation. Instead he blamed officials, claiming they had not told him the entire truth.
Business Secretary John Hutton told BBC One's The Politics Show: "I've known Michael Martin for a long time and I have a great deal of respect for him.
"He is a decent man and a good Speaker of the House of Commons and I am sure that is a position he will want to defend over the next few weeks."
Shadow home secretary David Davis said of Mr Martin: "Clearly he's got problems... The House of Commons has problems. It needs to be more transparent on these things."
But he said it was inappropriate for a member of a frontbench to comment on the Speaker's future.
Labour's Mrs Beckett said: "What I don't understand is why there have been a whole string of nasty little stories about Mr Martin. Somebody is out to get him."
Former home secretary David Blunkett told Sky News the Speaker had done a "pretty reasonable job" and described stories about him as a "witch-hunt". He called for MPs agitating for a resignation to "stand up and be counted".
However, former independent MP Martin Bell said: "MPs can talk about anything they like, inside or outside the House, except their views on the Speaker.
"They dare not speak out and we know that there is widespread disquiet on both sides of the House and no-one dares say a thing.
"So it's not a witch-hunt at all. I think he's being protected rather than hunted, actually."