Gordon Brown led moves today to shield Michael Martin, the Commons Speaker, from mounting pressure to step down after being drawn deeper into the controversy over MPs’ expenses.

In a show of support for the embattled Mr Martin, the Prime Minister told reporters during a visit to South London: “Michael Martin has been a very, very good Speaker.”

But Mr Brown stopped well short of endorsing him to remain in the post, saying in response to questions about the Speaker’s future: “This is a matter for the House of Commons.”

His praise for Mr Martin was echoed by a series of Ministers and ex-Ministers, who suggested that the Speaker was being unfairly singled out for criticism.

Alan Johnson, the Health Secretary, said: “I think it is a bit of an open season in some quarters on Michael Martin. I think it has been open season since he was elected to be Speaker.”

He told GMTV: “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.”

Tony Benn, the former Cabinet Minister, went much further, saying Mr Martin had been “very, very best” of the nine Speakers he had sat under when he was an MP and sought to defend him and his wife Mary against some of the criticism levelled at them.

“It’s a really tough job and he does it really, really well. The thing is he is a backbenchers’ speaker. Tony Blair did not want him as speaker but the House voted for him,” Mr Benn told GMTV.

“His wife has a lot of responsibility to undertake entertaining and they are trying to get at her. He is the first sheet metal worker to become speaker, it is supposed to be a very grand position.”

Nick Clegg, the Liberal Democrat leader, also spoke of a “witch-hunt” against the Speaker but was more guarded, saying he would have to answer the allegations being made against him.

Mr Clegg told a press conference that the controversy highlighted the need for an “utter overhaul” of the expenses and allowances paid to MPs.

But such shows of support and sympathy from Ministers and party leaders matter less to the position of the Speaker than it may appear, and were seen at Westminster as an attempt to draw the sting from the latest row - which risks damaging the reputation of all MPs - rather than to keep him in office.

Mr Martin cannot be removed from the Speaker’s chair by Ministers, or indeed by anyone, and requires the acquisition, if not the active support, of a critical mass of backbenchers from all parties if he is to stay beyond the short term.

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