The MPs expenses watchdog has revealed that a third of all MPs rent their offices from political parties, at a cost of £3.6 million to the taxpayer.
It is the first time such details have ever been made public, in what campaigners have described as “a back-door subsidy to political parties”.
The figures have been released by the Independent Parliamentary Standards Authority (Ipsa), which earlier this week warned that its revelations would be “the disinfectant that hurts as it heals”.
Between May 2010 and March this year, there were 244 office leases from a political party, compared with 477 which were not.
They included almost half of the Cabinet – among them Deputy Prime Minister Nick Clegg and the Conservative Education Secretary Michael Gove.
While Parliament’s rules state that MPs are allowed to rent offices from their political parties, they are subject to much stricter controls – particularly to ensure that they don’t pay over the odds.
Ipsa said that on average the costs of leases from political parties were noticeably higher than those from independent landlords – at £14,886 as opposed to £14,156.
The watchdog has now said it will be conducting a review of how MPs rent their offices, and that this discrepancy was one of the things they would be looking into.
Chairman Sir Ian Kennedy said: “Our rules allow MPs to rent from a political party - but we require an extra assurance from MPs if they do so: an independent valuation that the lease represents the market rate. We are confident that this measure means taxpayers have received value for money from these leases.
“As part of a broad review of accommodation support, Ipsa will consider whether, even if the individual leases are appropriate, the cumulative effect means we need to reconsider this aspect of the rules.”
Today’s figures showed that if the average cost of leases from political parties had been the same as those from other landlords, the bill for the taxpayer would have been £178,120 lower since the general election.
As well as Mr Clegg and Mr Gove, MPs who have claimed expenses to rent office space from their political party during this parliament include Lib Dem Danny Alexander, the shadow Justice Secretary Sadiq Khan and his Labour colleague Stella Creasy.
Among the Tories listed are Justice Secretary Chris Grayling, Health Secretary Jeremy Hunt, Work and Pensions Secretary Iain Duncan Smith and International Development Secretary Justine Greening.
Neither David Cameron nor Labour leader Ed Miliband rent from their parties.
Jonathan Isaby, political director of the TaxPayers' Alliance, said: “It's one thing if a local political party offers their MP and staff free use of a desk or an office, but quite another for it to be sending taxpayers an annual invoice for thousands of pounds.
“Often this is space that would not in any case be available to anyone else on commercial terms.
“The practice of MPs renting space from those who also donate money to the MP or their party should also set alarm bells ringing.
“It's effectively a back-door subsidy to political parties that is exploiting an allowance meant to assist MPs in their work serving their constituents, not boost the coffers of their re-election campaign.
“Individuals, businesses or trade unions should be free to provide office space to an MP as a donation-in-kind, but invoicing the taxpayer for that facility before then making a political donation appears to be little more than a sneaky way of channelling taxpayers' cash into party coffers.”