The disclosure caused his spokesman, Mike Granatt, to resign for "ethical reasons" after learning he had been misled into wrongly briefing a journalist.

He had been led to believe that Mary Martin had been accompanied by a Commons official on taxi trips for which she claimed more than £4,000 in taxpayer-funded allowances.

But Mr Granatt learned from the Mail on Sunday on Friday that that had not been the case and Mrs Martin had in fact been joined by a housekeeper. Officials who knew the truth of the matter had previously failed to point this out to him, he said.

Mr Granatt stressed that the Speaker, who is currently overseeing a review of MPs' expenses in the wake of the Derek Conway scandal, was not to blame for the misleading information.

A partner in the Luther Pendragon PR agency, Mr Granatt was officially media adviser to the House of Commons Commission, the management committee which Mr Martin chairs.

The revelation that Mrs Martin was only joined on taxpayer-funded taxi trips by her domestic help - with whom she is said to be good friends - will lead to fresh scrutiny of her allowances.

The suggestion that she had been accompanied by an official had appeared to bolster the defence that the journeys were on official business.

Home Office minister Tony McNulty said that allegations about MPs' expenses were being thrown around "like confetti".

He said: "I think Michael Martin has been a very good Speaker. The House of Commons has got an inquiry under way, by the Speaker, into all aspects of expenses. The sooner there is a greater transparency the better."