A bid to exempt Parliament from the Freedom of Information Act is this morning facing fierce cross-party criticism in the Commons.
Liberal Democrat Simon Hughes dubbed the move "seriously misguided" and "extremely bad politics".
Labour's David Winnick said it made a "mockery" of the House of Commons and would lead to the suspicion that MPs were trying to "hide" details of expenses and travel allowances.
He said that by not objecting to the Bill, there was "a suspicion that the Government is collaborating" with the sponsor of the Bill, Tory former chief whip and member of the House of Commons Commission, David Maclean.
Maclean's Freedom of Information (Amendment) Bill would exempt both the Commons and the Lords from the FOI Act's provisions and create a new exemption for all communications between MPs and public bodies.
But a small cross-party group of MPs has vowed to try to block the Bill in its report stage debate today, after it was "nodded through" without debate for its second reading.
Spearheading the opposition, Hughes said: "This is a very serious matter. It is a seriously misguided Bill.
"The previous proceedings, which have consisted of one hour in committee, have not revealed any facts justifying the need for the Bill.
"The present legislation works well. It would be extremely bad politics and extremely bad law for us at this stage – when Parliament is hardly the most well regarded institution in the land – to seek to exempt the Commons and the Lords from the FOI Act."
Winnick warned: "If this measure was passed into law, which hopefully it won't do, it would do a great disservice to MPs because inevitably the reaction will be – well of course MPs have something to hide, even if we haven't.
"The suspicion will be that we are trying to hide our expenses, travelling allowances and the rest of it."
Opponents of the Bill have tabled a series of amendments to try to block it. As they began debate on the first group, Hughes said it was a "fundamentally mistaken proposition" to try to exempt information about MPs' expenses from FOI rules.
Hughes said a key benefit of the current system was that MPs were forced to be "more accountable" because their activities were in the public domain.
"One of the things that the public are saying to all of us is they want us to be as accountable as possible. They want to know what we are doing and in particular they want to know how we spend money on their behalf," he added.
"I don't think it is good enough for us to say that we should decide whether we are going to follow that principle by law."
Hughes continued: "I think it would be regarded as completely beyond acceptable if we said you can't know some or all of the information about what we do."
Private Members' Bills can be blocked by "filibustering" – a tactic to delay or prevent their passage by prolonging debate to block a vote.
To stop his Bill being "talked out", Maclean will need 100 MPs to force a closure vote enabling it to be sent to the Lords.
However, it is doubtful that he will be able to muster that many MPs on a Friday when most have returned to their constituencies.
The Government has said it has no official position on the Bill, but its lack of opposition to date suggests a tacit approval.