John Bercow, the Commons Speaker, has asked the parliamentary expenses watchdog not to publish official documents which identify MPs' landlords.
Publication of the names, which was supposed to take place on Thursday, may have exposed any MPs who were renting their homes to one another. The loophole means MPs can build up capital in property at taxpayers' expense, despite official attempts to stop the practice after the expenses scandal.
Sources at the expenses regulator said a small number of MPs rented their properties to one another.
In a letter released on Wednesday night, Bercow wrote to the Independent Parliamentary Standards Authority (Ipsa) claiming that publication of the landlords' details jeopardised their security and had led to "grave concerns" in the House of Commons.
"The processing of the data … could involve causing unwarranted damage and distress," the Speaker wrote. "I should be grateful if you and your colleagues would reconsider such a plan."
Sources at Ipsa said there were genuine concerns that it would be possible to identify MPs' homes if their landlords' names were released.
MPs believe that by using the internet and the land registry, it may be possible to work out where they live. This is being investigated by Ipsa, before it replies to Bercow.
The Speaker acknowledged MPs' concerns in parliament on Wednesday. His letter states that the issues surrounding security are backed by the Serjeant of Arms and the parliamentary security director.
Dr Julian Lewis, a Conservative MP, disclosed in the Commons that freedom of information laws were being used to release the documents.
"You'll remember the long campaign successfully waged three years ago to ensure that members of parliament's addresses would never be disclosed as a result of FoI requests," he said. "A number of colleagues from both sides of the House have approached me about an FoI request that those colleagues who, unlike me, rent their properties, should have their landlords' names disclosed. There is concern that this could breach the security of MPs' home addresses."
There have been increasing concerns over MPs' security since Stephen Timms, the Labour MP for East Ham, was stabbed in his surgery by the Islamist Roshonara Choudhry in May 2010.
Some politicians have complained that their homes have been identified by extremist groups and been subjected to attacks. Sajjad Karim, the Tory MEP for the North West, said last year that his family felt threatened by English Defence League members who congregated outside his home.
Bercow's letter has echoes of the attempt by the previous Speaker, Lord Martin, to prevent the release of addresses on which parliamentary expenses were claimed. The information was subsequently sold to the Daily Telegraph, causing the scandal that led to the resignation or prosecution of dozens of MPs. Martin had to resign after fighting to keep information about expenses secret.
Ipsa banned MPs from claiming back mortgage interest after a transitional period, which ended this summer. This followed concerns that politicians were able to build up valuable property empires at taxpayers' expense.
Its initial rules banned MPs from renting properties from family members, close business associates or "an organisation in which you or a family have an interest". This was to help to ensure that MPs did not claim the market value for rent from the taxpayer while actually paying far less.
The rules were later clarified to allow one MP to rent from another, provided they were not related or married. It is thought that this rule was specified following requests from MPs.
A stolen computer disc sold to the Daily Telegraph disclosed the existence of a "property merry-go-round", with dozens of MPs renting out their previously taxpayer-funded homes and immediately renting nearby homes, claiming the new rental costs from the taxpayer.
David Laws, the Liberal Democrat minister, was forced to resign and repay tens of thousands of pounds after being exposed for paying rent to his boyfriend.
A spokesman for the House of Commons said Bercow's letter "relates solely to the security implications of publishing MP rental details based on professional advice and resolutions of the House. Neither the Speaker nor the House of Commons has knowledge of MP rental arrangements — the rules governing MPs' accommodation are a matter for Ipsa and have been since 2010."
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