Commons Speaker spent £21,516 of taxpayers' money to 'challenge negative press'

Mr Martin employed libel firm Carter-Ruck for three months following unflattering newspaper reports questioning his impartiality and conduct.

Another article claimed his wife Mary had been given special dispensation from the strict security checks that non-MPs must undergo to enter Parliament.

Mr Martin is thought to be the first Commons Speaker to hire lawyers as spokesmen.

Reporters who tried to contact him over the summer were referred to Carter-Ruck. His predecessor, Betty Boothroyd, instructed her secretary to deal with inquiries.

Yesterday, official figures showed the bill for Mr Martin's legal advice was accrued during June, July and August.

The TaxPayers' Alliance campaign group accused him of adopting 'the airs and graces of the ancien regime'.

Chief executive Matthew Elliott said: "By using our money to defend himself against his critics and to soothe his thin skin, he is showing contempt to taxpayers.

"If he wants to hire flunkies, he should pay for them himself and not expect us to pick up the tab.

"He should not forget how far £21,000 could go to help taxpayers in his home town of Glasgow."

Liberal Democrat MP Norman Baker expressed alarm at the size of the bill and the willingness of the Commons authorities to approve the expenditure.

He said: "This is a deeply worrying figure. Of course it's right that there should be legal advice available to all members of the House of Commons.

"But it appears the very expensive Carter-Ruck has effectively been used to issue press releases and that those instructing them have been content to sign blank cheques irrespective of the cost to the taxpayer."

Mr Martin, a former trade unionist and sheet metal worker, earns £136,677 a year for presiding over Parliamentary debates.

But he has attracted sustained criticism for some of his rulings.

He prompted uproar last year when he prevented David Cameron from asking a question about the future leadership of the Labour Party, claiming he should ask Tony Blair only about the actions of the Government.

He also tried to stop details of MPs' £5million a year travel expenses from being revealed.

The House of Commons Commission, which is chaired by Mr Martin and oversees Parliamentary business, spent £17,300 unsuccessfully trying to block the freedom of information request.

Nick Harvey, MPs' representative on the Commission, disclosed Carter-Ruck's bills.

He said: "During July and August, the House administration endorsed the Speaker's use of the firm Carter-Ruck to counteract a series of articles that were published in the media which questioned the impartiality of the Speaker in his official role.

"The cost of this advice was £18,696.06."

A spokesman for the Commission, which is now dealing with the Speaker's media inquiries, confirmed the money would come from public funds, as would an earlier bill of £2,820 for work carried out by Carter-Ruck in June.