MPs have backed a bid to ensure that their correspondence is exempt from freedom of information laws.

Former Conservative chief whip David Maclean's controversial Freedom of Information (Amendment) Bill was debated in the Commons on Friday.

Despite vigorous opposition from some MPs, it was passed at its third reading by 96 votes to 25 and will now move to the House of Lords for further consideration.

Opponents of his measure, who had already made one attempt to block it, argued that it is hypocritical for MPs to exempt themselves from laws they have applied to other public sector bodies.

But supporters said that the privacy of correspondence between constituents and MPs must be protected.

The Liberal Democrats led the opposition, and leader Sir Menzies Campbell called on the chancellor to oppose the Bill.

"In recent days, Gordon Brown has spoken out about the need to restore the reputation of Parliament and for more openness and transparency, and that's quite right," he told BBC Radio 4's Today programme.

"But these objectives are hardly likely to be served if we have one law for MPs and one for everyone else.

"There is already protection under the Data Protection Act and the freedom of information legislation itself provides protection.

"If there is concern about the nature of the sanctions for any breach, we can do that by altering the Data Protection Act."

Speaking in the Commons, justice minister Bridget Prentice said the government was "neutral" on the bill.

"It is for Parliament to discuss and not a matter for the government," she said.

The minister also accused the Lib Dems of "party political grandstanding" in their approach to the legislation.

Labour's David Winnick, meanwhile, said that the legislation would "inevitably spread suspicion" about the actions of MPs.

But defending his Bill, MacLean said it was vital for MPs to be able to guarantee the confidentiality of cases they are dealing with on behalf of constituents.

"We cannot give that guarantee at the moment," he warned.