The battle over MPs' expenses claims is heading for the High Court after the House of Commons launched a last-ditch bid to avoid disclosure.
The decision to appeal, over MPs' concerns that the publication of their addresses would present a security risk, prompted questions about the potential bill to the taxpayer.
A spokeswoman said MPs feared that if their second home addresses were published they would be less inclined to speak their minds, which would "inhibit democratic debate".
The move is the latest twist in a three-year battle between the Commons and freedom of information campaigners for the release of the details of 14 MPs' Additional Costs Allowance (ACA). It emerged earlier this month that the £23,000-a-year allowance can be used for a whole range of household items, including £10,000 kitchens and £6,000 bathrooms.
The Information Tribunal recently ordered the Commons to release the MPs' individual claims and said there was no reason why their second home addresses should not be revealed too. But, after failing to secure a week-long extension to the March 25 deadline for disclosure, the Commons lodged an appeal on Tuesday afternoon.
Commons Speaker Michael Martin is said to have been "mindful" of MPs' concerns and took advice from the security services.
A spokeswoman for the Commons Commission, which manages House affairs, said: "Having received advice he's concerned that the Information Tribunal may have misdirected itself in law in deciding that home addresses of MPs should always be published subject to only limited exceptions."
The Commons also considered that the tribunal gave "insufficient attention to the reasonable expectations" of MPs.
"The threats that MPs can face are unpredictable and subject to change," the spokeswoman said, adding that release of their home addresses could "inhibit democratic debate" on a range of sensitive issues.
But campaigner Heather Brooke, who has been fighting for the information's release, criticised the move, saying: "They have had 28 days to do this so why the last-minute theatrical farce? And what a shocking waste of taxpayers' money. The people who are keeping things secret are being subsidised by the taxpayer."
