More than £100,000 a year has been spent on average on items including furniture, art and air conditioning for the Grade 1-listed apartments.

The figures were released to the Daily Telegraph under the Freedom of Information Act and come as the Speaker is under intense pressure over MPs' expenses.

They show that £148,900 has been spent on furniture, £191,000 on a new air-conditioning system, £13,000 on art and £291,000 on "building restoration and refurbishment" in Speaker's House.

In total, £724,000 has been spent on the residence - which also includes the State Rooms of the Palace of Westminster - since 2001. Mr Martin was elected Speaker in October 2000.

Another £992,000 has been spent on Speaker's Garden, although most of the costs have gone on improving security since 9/11. Security costs for the Palace as a whole have escalated since 2001.

Mr Martin's spokeswoman said the spending was part of a rolling programme of improvements which were commissioned by the Parliamentary Estates Directorate.

The Speaker has already come under fire for claiming more than £75,000 of second homes allowance on his Glasgow property, for which he has no mortgage.

In the last week, the House of Commons Commission - which the Speaker chairs - has faced criticism from MPs for launching a High Court appeal against the release of a detailed breakdown of MPs' second home claims.

Mr Martin, a former sheet metal worker who now earns £138,000 a year, has barred MPs from talking about the legal bid in the Commons.