Lord Mandelson stoked up the row over the arrest of MP Damian Green by accusing the Conservatives today of using it as a "smokescreen" to cover their party's alleged collusion in a breach of the law.
While accepting there was real anger among Tory MPs over Mr Green's arrest and the police search of his Commons office, the Business Secretary said much of the furore was a "self-serving" attempt to distract attention from the offences he is suspected of committing.
Senior Conservative backbenchers are expected to lead demands for a full debate on the affair after Speaker Michael Martin makes a statement to the Commons at 2.30pm today, following the Queen's Speech.
Mr Martin will set out the events of last Thursday and try to justify allowing police to carry out the search, which many across the parties regard as a breach of parliamentary privilege.
Fireworks are expected if the Speaker attempts to restrict questions to short points of order, as aides suggest he will.
A number of Tories are considering the "nuclear option" of tabling a motion of no confidence in the Speaker, which could potentially pave the way for his removal.
But it is thought unlikely that MPs will seek to disrupt the Queen's Speech, which sets out the Government's legislative programme for the coming year and is the ceremonial highpoint of the parliamentary calendar.
Speaking on BBC Radio 4's Today programme this morning, Lord Mandelson suggested that some of the outrage being expressed by Tory MPs over the police raid was concocted.
He said: "The separate and equally important issue is the apparent relationship between the Opposition and a Home Office official who, in an attempt to pursue his political ambitions in the Conservative Party, allegedly, systematically passed sensitive and classified Home Office papers to the Conservative Party, apparently in the full knowledge of the Conservative front bench and in complete breach of the Civil Service Code and the law.
"So whilst I recognise that the anger being expressed by some MPs is no doubt sincerely felt by some of them, I also think it is pretty self-serving by Conservative MPs who want to put up a smokescreen to hide their own party's role in allegedly colluding with a Home Office official in breaking the law."
Today's showdown comes as the controversy over Mr Green's arrest in connection with Whitehall leaks deepened.
The Ashford MP denies all wrongdoing, and has been released on police bail until February. Civil servant Christopher Galley, 26, who insists that he passed papers to the Tory immigration spokesman in the public interest, was arrested and bailed last month.
Home Secretary Jacqui Smith lashed out at the Tories last night for lacking "respect" for the law.
She angrily dismissed suggestions that she was not being straight with the public over what she knew about the investigation.
No one in her department had been aware an MP was involved until 1.45pm on Thursday afternoon, she stated.
"I am, of course, prepared to restate all of this on the record in Parliament, and I will be seeking to make a statement at the earliest opportunity," wrote Ms Smith in a letter to her Tory shadow Dominic Grieve.
Last night the Tories upped their attack over Mr Green's treatment by releasing footage of police arriving to carry out the raid.
Mr Grieve said the images documented a "dark day for democracy".
"MPs are not above the law," he said. "But they must be allowed to bring the Government to account and to put into the public domain information which may be uncomfortable for ministers."
Mr Grieve welcomed Ms Smith's admission of "complete ignorance" over the involvement of an MP in the inquiry - but demanded more information about "who in Government knew what, and when".
Ms Smith condemned the Tories for attempting to play down the significance of the alleged crimes of which Mr Green and Mr Galley are suspected.
"Rather than seek to dismiss the offence the police are investigating as 'an antiquated common law misconduct offence', you would do better to show respect for the law and the duty of parliamentarians to uphold the law," she wrote.
She insisted it was vital to prevent leaks from the Home Office, and that principle extended "not just to matters of national security or otherwise covered by the Official Secrets Act".
Labour former minister Denis MacShane demanded an explanation from Tory leader David Cameron of his spokesman's dealings with Mr Galley.
"The police should have never have invaded Parliament last week but the Tories are turning a question of parliamentary privilege into a sordid effort to extract maximum party political capital out of the affair," he said.
"MPs' anger and concern over the police raid will be vitiated until Mr Cameron comes clean on what was going on between Mr Green and the man who betrayed his duty of loyal service to the minister who trusted him."