Campaigner Heather Brooke hailed the ruling as victory for accountability
The House of Commons has lost its High Court battle against a decision to force disclosure of MPs' expenses.
The Commons challenged the Information Tribunal's "unlawfully intrusive" demand that a detailed breakdown of second home allowances must be given.
It also failed to overturn the decision that MPs' addresses could be published.
The Commons must release the details by next Friday. Gordon Brown's spokesman said the PM was "relaxed" about his expenses being published.
But he added that there were security "issues" about giving out MPs' addresses.
Shadow Chancellor George Osborne, who is not one of the 14 MPs covered by the original Freedom of Information request, said MPs had to be "open and accountable" with public money.
"I am very happy for people to see how I have spent the allowances," he told BBC News.
Lib Dem leader Nick Clegg, who this week published details of his allowances, said it was "vitally important" the public could have "complete confidence in the expenses system".
"There is an urgent need to overhaul the system of claiming expenses to restore public trust, including independent spot checks and a requirement for receipts for every penny of public money spent," said Mr Clegg.
The Lib Dem front bench will publish details of their expenses from July onwards.
The Commons has until 1200 BST on Tuesday to appeal against the High Court ruling.
The Members' Estimates Committee, the body which deals with MPs' pay and allowances, is due to meet beforehand to decide whether to take the case any further.
The Freedom of Information (FOI) request at the centre of the dispute asks for a detailed receipt-by-receipt breakdown of expenses for 14 MPs and former MPs, including Mr Brown and Tory leader David Cameron.
The Commons authorities argued that full disclosure would lead to MPs' home addresses being released which it said should be barred on security grounds.
But this argument was rejected by the High Court in its ruling.
It said: "An individual who is determined to discover the residential address of an adult, law-abiding citizen is likely to be able to do so by one legal means or another.
"And where the person concerned is a holder of public office and in the public eye, an inquiry is likely to be easier."
The Commons authorities have also been ordered to pay at least £33,500 in costs.
'Right to know'
The High Court ruling is a victory for journalists and information freedom campaigners Heather Brooke, Ben Leapman and Jonathan Ungoed-Thomas.
Giving her reaction outside the High Court, Ms Brooke said: "This ruling makes clear that in a democracy it is the people who are the masters and politicians must be directly accountable to them.
"Anyone making a claim on the public purse must be prepared to put forward their receipts to justify their expenses and to make those receipts public."
The ruling was also welcomed by the Information Commissioner's Office.
Deputy commissioner Graham Smith said: "MPs claim expenses in relation to their public duties and the public therefore has a right to know what that money is spent on."
He said the ruling would also "serve as a useful point of reference" when the commissioner considered future FOI cases.
The Hansard Society said the ruling was important for parliamentary democracy and accountability.
"At a time when trust in our elected representatives is at a very low ebb it is important that politicians are accountable to the public they serve and are seen to be bound by the same conventions as the electorate," said deputy chief executive Alex Boughton.
Under their "additional costs allowance", MPs can claim up to £23,000 a year towards the cost of maintaining a second residence, normally in their constituency.
The allowance covers expenditure incurred when an MP is away from home on parliamentary duties, such as the cost of furniture and household bills.
'John Lewis list'
The original demand for a detailed breakdown of the additional costs allowances of 14 MPs and former MPs was made under the Freedom of Information Act.
The Information Tribunal said the breakdown should be given, but the battle was then taken to the High Court by the Commons Commission.
MPs were criticised when the so-called "John Lewis list" of household items was published earlier this year.
All of them could be bought using the second home allowance, and included £10,000 kitchens and £6,000 bathrooms.
Commons Speaker Michael Martin was himself criticised when it emerged that his wife had claimed £4,139 on taxis - largely for shopping trips.
But on Wednesday, Parliament's standards chief John Lyon ruled Mary Martin's claims were "reasonable".