The House authorities had argued that proving a breakdown of the outlay by seven MPs in Wales would breach their privacy.

But Commissioner Richard Thomas decided the material was not exempt and it must be disclosed.

MPs can claim for producing and distributing circulars and reports to constituents under the Incidental Expenses Provision (IEP).

However, the House only publishes a global figure for each MP's spending from the allowance - which also covers a variety of other office costs, and some travel and staff expenditure.

Critics claim the IEP is exploited by some members to produce political mailshots.

According the Commissioner's ruling, the Commons argued that it would be "unfair" to disclose the material because MPs had been given "no notice".

But the ruling rejected the Commons' objections, insisting that MPs should have expected their spending to be scrutinised.

He said: "In this case, the expenses details held by the House relate to MPs' official duties and exclude personal or political activities.

"In this respect, the Commissioner believes that MPs must have the expectation that their public actions will be subject to greater scrutiny than would be the case in respect of their private lives."