MPs expenses: Row over disclosure of MPs' letting details
MPs are trying to block publication of material which could show they are renting their taxpayer-funded homes to each other, it is claimed.
Expenses watchdog The Independent Parliamentary Standards Authority is considering a Freedom of Information request to release the details.
Commons Speaker John Bercow said publication would be a "security risk".
The BBC has been told that four MPs are currently sub-letting their second homes to other MPs.
The practice is within the rules on second homes, which were overhauled after the expenses scandal in 2009.
IPSA, the external regulator which took over responsibility for MPs' expenses in 2010, is due to release routine details of expenses claims on Thursday.
However, Mr Bercow has sparked a row by writing to IPSA's chairman Sir Ian Kennedy urging him not to publish details of MPs landlords and agents in relation to their subsidised second homes.
In the letter, he says he understands that a request had been made under Freedom of Information laws for the details to be made public.
Although he did not known the "precise" nature of the request, he said a number of MPs had expressed "grave concerns" about such "personal" information being published.
"Their concerns are shared by the Serjeant At Arms and Parliamentary Security Director who believe there is a very real danger that the release of this information could lead to the unnecessary discovery of members' residential addresses and this could provide a security risk," he wrote.
Such information is exempt under FOI laws, Mr Bercow adds, and the principle of upholding data protection rights should take precedence over any public interest in releasing the information - since doing so "would/might expose members to risk".
"If IPSA is planning to release the information...I should be grateful if you and your colleagues would consider such a plan."
A Commons spokesman said the 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."
'Bad old days'
There is no rule barring MPs from sub-letting properties to colleagues.
The rules governing what claims MPs can make on their second homes - paid from the public purse to enable them to fulfil their dual parliamentary and constituency duties - and how many are eligible for the allowance were overhauled in 2010.
This followed revelations that many MPs had made inappropriate claims under the old system, administered by Parliament, and a handful had committed fraud.
Labour MP John Mann told the Daily Telegraph, whose expose of MPs' claims led to the changes, that although there was nothing wrong with the practice of sub-letting, details of such arrangements should be out in the open.
He added: "I have no problem in MPs renting it out but the public is entitled to know that...There is a way to get the information out to satisfy the general public. The media will want to know if there are any scams going on."
'Against the law'
Conservative MP Julian Lewis said it was against the law for MPs' home addresses to be published but that releasing details about their landlords - when combined with basic postcode information - could enable people to discover where they lived, raising potential security problems.
He defended Mr Bercow, saying the Speaker was only attempting to ensure the law was upheld.
"Everyone accepts that MPs' addresses, by law, must not be revealed," he told BBC Two's Daily Politics.
"All the Speaker is trying to do is to stop a way that...could lead to the undermining of the existing legal position which is the MPs' personal addresses for very good security reasons should not be revealed...That is the law as it is."
Many MPs, he added, faced having to either sell their properties or rent them out following changes to the rules barring them from claiming interest on their mortgage payments.
"If they did not rent to each other, they would probably just rent to some other member of the public...I personally don't think it looks good for MPs to be scratching each other's backs in this way but if that is right, the fault lies with IPSA."
Asked whether David Cameron was concerned about reports of MPs renting their flats to one another, a Downing Street spokeswoman said: "As you know, the prime minister is committed to transparency, but this is a matter for IPSA."