Prime Minister Gordon Brown today led support for beleaguered Commons Speaker Michael Martin.
He said the Glasgow North East MP "has been a very, very good Speaker".
And Liberal Democrat leader Nick Clegg said there had been "something of a witch-hunt" against Mr Martin, who takes the chair in the Commons this afternoon after a torrid weekend of newspaper headlines.
Critics have urged the Speaker to hand over control of a review of MPs' allowances after fresh questions arose over those claimed by him and his wife, Mary.
The disclosure that his office deceived the public over Mrs Martin's taxpayer-funded taxi journeys caused his spokesman, Mike Granatt, to resign for "ethical reasons" at the weekend.
The Parliamentary Commissioner for Standards is being urged to investigate the revelation that Mrs Martin had not been accompanied on the trips by a Commons official, as journalists had been told.
There was also concern over Mr Martin's use of the second home allowance after it emerged that he has no mortgage on a property for which he has claimed more than £75,000 to maintain.
He is already under fire for using air miles earned on official business to pay for flights by family members.
On a visit in south London today, Mr Brown told reporters: "This is a matter for the House of Commons.
"Michael Martin has been a very, very good Speaker."
Mr Clegg insisted he would not give a "running commentary" on Mr Martin's position, and said the Speaker would have to "answer" the allegations.
But he told a press conference in Westminster: "Worryingly, (it) looks like something of a witch-hunt against him."
The criticism also highlighted the need for an "utter overhaul" of the Parliamentary expenses system, he said.
Health Secretary Alan Johnson also gave his support to Mr Martin.
"I think it is a bit of an open season in some quarters on Michael Martin," he told GMTV.
"I think it has been open season since he was elected to be Speaker.
"Yes, I do support the Speaker and I do think this will blow over and the people who are, in some quarters of the press, who are obsessed about Michael Martin will move on and pick on someone else."
Mr Martin is chairman of the Members Estimate Committee, which instigated a "root-and-branch" review of expenses in the wake of the Derek Conway affair.
Mr Conway (Old Bexley and Sidcup), a Tory MP until he was stripped of the party whip after being censured for overpaying his son out of allowances, is eligible to return to the Commons today after a 10-day suspension.