Michael Martin, the Commons Speaker, was yesterday cleared of misusing public funds after his wife Mary spent more than £4000 on taxi journeys to buy food and other goods for her husband.

John Lyon, Westminster's sleaze watchdog, dismissed a complaint from campaign group the Taxpayers' Alliance, making clear that her taxi journeys were "reasonable in all the circumstances".

Indeed, it was revealed that, under the rules, Mrs Martin could have spent not the £4139 she did over four years to this February, but as much as £10,000 as the annual limit is £2500.

The Standards Commissioner explained the Martins had been offered the use of taxis by a previous Clerk of the House to help the Speaker in his work. The "tremendous pressures" of his duties meant Mr Martin could not normally leave parliament. It was made clear neither he nor his wife had asked for the taxi facility.

The report noted Mrs Martin did not drive and the "alternative" to using taxis, the UK Government's own chauffeur-driven car service, was more expensive. The Speaker's wife took 146 taxi journeys over four years.

"The events ranged from meetings to private conversations," said the report, but all hospitality provided was "conducted in the course of his official duties".

On taxi journeys to the supermarket, the cab waited for Mrs Martin and her official housekeeper and returned them with their purchases to the Commons.

As well as journeys to the supermarket, there were up to 39 annual visits to smaller shops. Mrs Martin bought "further provisions and perishables", including clothes and table decorations. On these occasions, the cab did not wait and she paid to return. "None of the journeys was for her own use or entertainment," said the report.

There was a very small number of other journeys: two were to the Martins' personal residence in London to store documents and one was to a builder's merchants with an official from the Commons maintenance department to choose materials for work on the Speaker's House.

Mr Lyon concluded that, given the alternative, the costs of Mrs Martin's taxi journeys were "not excessive" but "reasonable in all the circumstances".

The complaint was made in February by Mark Wallace of the Taxpayers' Alliance after reports Mr Martin "abused" his allowances and the use of taxis by his wife might not have been in line with MPs' code of conduct.

Earlier this year, the row led to the resignation of Mike Granatt, the Speaker's spokesman, who said he had inadvertently misled journalists over the details of the shopping trips after being misinformed by the Speaker's officials.

He had been led to believe Mrs Martin had been accompanied by a Commons administrative official when in fact she had been joined by her housekeeper.

Mr Lyon said he was "disturbed and concerned" to see his letter to Mr Wallace, saying he would investigate his complaint and marked "personal and confidential", had been released to the press. "That was not done by my office," insisted the commissioner.

"Such release is not fair on the member who abides by the confidentiality provisions during the course of the investigation and risks inaccurate speculation about my investigations which only hamper the work and confuse the public."

The report also revealed Mr Martin had expressed concern at the leaked letter, saying it denigrated his wife's character without a right of reply. In releasing Mr Lyon's report, the Commons standards and privileges committee said it too "deprecated" the leak. The MPs made clear they had "no hesitation in endorsing" the commissioner's dismissal of the complaint.

Last night, Mr Wallace said Mrs Martin's taxi journeys appeared to be "more for food for the Martins than for official functions".

He went on: "If so, it's shocking that they are able to use taxpayers' money for taxis to do their domestic grocery shopping. If this is within the rules, then the rules urgently need tightening up."

The Speaker is currently heading up an inquiry into the future of MPs' expenses, due to report before the summer.