Detectives accused Damian Green of “grooming” a young civil servant during questioning over the leaking of up to 20 Home Office documents, according to a senior Conservative.

The row over the arrest of the Tory frontbencher escalated last night as Jacqui Smith, the Home Secretary, and Michael Martin, the Speaker, came under pressure to explain further their roles in the affair.

Ms Smith’s claim not to know that a Tory MP was under investigation was directly challenged by her Shadow, Dominic Grieve. Mr Martin was forced to announce that he would make a Commons statement on why the police were allowed to raid Mr Green’s parliamentary office.

In a welter of briefings from police, ministers, civil servants and Commons officials, the most incendiary came from a senior Conservative who said that Mr Green was accused of “grooming his contact” during his nine-hour detention on Thursday. “Damian was very angry at this clear attempt to provoke him and did not reply. As a party we want to make it clear that this was grossly inappropriate but symptomatic of the cack-handed way the police have conducted this investigation.”

Sources close to the investigation confirmed that they were examining information suggesting that Mr Green encouraged the official, Christopher Galley, 26, to leak documents and may have set him specific tasks.

The Metropolitan Police are investigating claims that Mr Galley, who stood as a Conservative candidate in a council election, sought out Mr Green at a party event. They are also likely to be studying any reply to a letter he sent asking for a job with Mr Green. Senior civil servants said that about 20 leaks were being investigated. The Tories had put the figure at four.

Ms Smith refused to apologise for the manner of Mr Green’s arrest. She said that the investigation was triggered by “a systematic series of leaks from a department that deals with some of the most sensitive and confidential information in Government”.

Mr Grieve alleged that she “knew very well” that an MP was being drawn into the investigation, but “just decided to sit back on her hands”. The Shadow Home Secretary rejected Ms Smith’s claim that it was proper that ministers kept out of police investigations, saying that “all sense of proportion and common sense” had been lost. The police appeared to have been acting on “flimsy and trivial grounds”, he said.

The Speaker said that he would make a statement after Harriet Harman, the Leader of the House, questioned the decision to allow police to search Mr Green’s Commons office. Mr Martin faces questions over whether he personally approved the raids and on what basis.

Sir Paul Stephenson, who becomes acting commissioner of the Metropolitan Police today, may withdraw an application to be the next commissioner after a row with Boris Johnson, the London Mayor, over Mr Green’s arrest. One Yard source said: “This is the worst crisis ever — if we call off the inquiry we look stupid and if we go ahead the criticism will be relentless."

Gordon Brown was told that a Home Office mole had been caught before Mr Green was arrested. Treasury officials refuse to say formally whether there is a leak inquiry into the disclosure of information from No 11, including details of the Pre-Budget Report. A source said that the investigation was internal and that the police were not involved as yet.

Other Home Office leaks being investigated are: the complete version of Sir Ronnie Flanagan’s report on the future of policing in February; the information that a disc containing details of 4,000 Dutch offenders that had been sent to Britain had been lost for a year; and news of the loss of data on thousands of prolific offenders.

The leak in August this year that a memory stick containing names of prolific offenders and the names and addresses of 84,000 prisoners had been lost was particularly damaging as it was disclosed just two days after Ms Smith herself was informed.

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