The House of Commons Speaker John Bercow is trying to block the publication of details of MPs' expenses which could show if they are renting their taxpayer-funded homes to each other, it has been reported.
Mr Bercow has written to the regulator urging it not to release documents revealing the identities of MPs' landlords for security reasons, according to The Daily Telegraph.
The newspaper said disclosure would expose the extent to which MPs are taking advantage of a "loophole" which allows them to rent properties to each other.
It said the concession meant MPs could still build up property nest eggs at the taxpayer's expense, despite moves to stamp out the practice follow the expenses scandal.
However Mr Bercow was said to have written to the Independent Parliamentary Standards Authority (Ipsa) warning that its plan to reveal the identities of MPs' landlords had given rise to "grave concerns" about security.
The Telegraph quoted the letter as saying: "The processing of the data ... could involve causing unwarranted damage and distress. I should be grateful if you and your colleagues would reconsider such a plan."
Labour MP John Mann said the attempt to prevent the publication of the details appeared to be a "return to the bad old days". He told the paper: "If MPs are renting from past or current MPs it is right and proper the public is able to know that."
"There is nothing wrong with that, and there is nothing wrong in it being out there in the open. I have no problem in MPs renting it (a flat) out but the public is entitled to know that."
A spokesman for Ipsa told the Telegraph: "We are committed to transparency as is shown by our regular publication of all claims by all MPs. We have a duty to balance that against the risk of compromising security. We are currently going through the process of gathering all the relevant information to get that judgment right."
A spokesman for the House of Commons said: "The Speaker's letter to Sir Ian Kennedy, chair of Ipsa, 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."
The Press Association, photo by Office of Governor Patrick