The Home Office "mole" at the centre of the police investigation into government leaks yesterday confessed to passing low-grade information to Conservative shadow minister Damian Green in the belief that it would be used "in a responsible manner in the public interest".

At a press conference conducted on his behalf by his lawyer, Christopher Galley, a 26-year-old Home Office civil servant, called on the authorities "not to shoot the messenger" in what was seen as an attempt to bind his fate with the politician to whom he gave material.

Mr Galley was arrested 13 days ago after Home Office material was allegedly passed to Mr Green, the Conservative immigration spokesman.

Mr Green was himself arrested by police last Thursday on suspicion of conspiring to commit misconduct in a public office, and held for nine hours while his home and Westminster office were raided.

Tory sources say he was outraged to be accused by officers of "grooming" Mr Galley and obtaining up to 20 documents. Both men have been released on bail pending further questioning early next year.

The incident has caused outrage among parliamentarians, and furious Conservatives have demanded an apology from the Home Secretary and a statement from the Speaker of the Commons. The latter is expected tomorrow.

Last night the Conservatives accused the government of colluding with the Commons authorities and senior civil servants to stage-manage the Speaker's statement, after a Cabinet Office e-mail inviting ministers and civil servants to a meeting to discuss the issue was leaked to them.

"It is completely improper to convene a meeting privately without any representation from other parliamentarians," said shadow home secretary Dominic Grieve. "We insist on being present along with representatives of all political parties."

Earlier Mr Grieve launched a personal attack on the Home Secretary Jacqui Smith, accusing her of failing in her duty to take responsibility for the arrest of his colleague.

In a clear sign that the Conservatives are determined to turn the issue into a major political row, the opposition also maintained fire on the Speaker of the Commons, Michael Martin, who they believe should have refused the police access to Mr Green's office in Westminster.

Tory backbencher David Wilshire made a formal complaint to the Speaker that the raid breached a ban on agents of the Crown entering the Commons, which was imposed after Charles I sent soldiers in to arrest MPs in 1642.

MPs on both sides of the House have protested that the arrest of a fellow MP and the search of his Westminster offices undermines the democratic basis of parliamentary scrutiny.

Nick Clegg, the LibDem leader, also revealed that he had been in contact with David Cameron's office to discuss tactics over this issue.

He said the Liberal Democrats had not ruled out joining the Tories in a protest on the floor of the Commons tomorrow after the Queen's state opening of parliament. Co-ordinated action is being planned by the former shadow home secretary David Davis.

Both the Prime Minister and the Home Secretary have denied having prior knowledge of Mr Green's arrest, although the Speaker, Tory leader David Cameron and the chair of the Metropolitan police authority, Mayor Boris Johnson, were all informed.

Downing Street has refused to comment directly on the case. The Prime Minister's spokesman said yesterday there were a number of important principles that needed to be considered, and that there would be a time when specific issues arising from the investigation could be discussed.

"The law shouldn't interfere with MPs doing their job. But it is also the case that MPs are not above the law," said the spokesman.

Mr Galley was unable to speak at his press conference as he is still under active investigation.

His solicitor, Neil O'May, confirmed that Mr Galley, who was a Conservative activist and is believed to have applied for jobs in Mr Green's office before entering the civil service, had met with Mr Green in parliament in 2006 and spoken to him a number of times over the following two years.

He denied reports that after his arrest Mr Galley had been knowingly used by police to entrap Mr Green.

Mr O'May said the investigation was "pretty extraordinary when you look at the kind of material that was passed across and the damage, if I can say that, done to the government".

The Official Secrets Act had not been breached, he said.

Meanwhile, the House of Commons Public Administration Committee announced plans for its own inquiry into the wider issue of the handling of leaks from Whitehall departments.

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