Officers from the Metropolitan Police told an MP that he could go to jail for life if he was found guilty of facilitating leaks from the Home Office.
Shadow immigration minister Damian Green gave evidence to a committee of MPs this afternoon about his arrest last year.
The Conservative MP for Ashford said on November 23 he was detained by the Metropolitan Police in a room, in a police station rather than a cell, and was not handcuffed.
He was at a police station for nine hours and questioned by the police in two separate interviews.
A special Commons committee on the issue of parliamentary privilege was considering Green's treatment this afternoon.
Green was asked by committee chair Sir Menzies Campbell if the police told him the charge he faced, of misconduct in a public office, can lead to life sentence.
"I was told by police that I faced life imprisonment," he confirmed.
"I thought it was ludicrous."
Green said there was a clear attempt to "get round" the changes to the Official Secrets Act made in 1989 and "someone" had looked for a common law offence to bring back a criminal sanction against leaking.
"Parliament made its views very clear in 1989, and it seems to me that attempting to recreate that offence has failed," Green said.
He added that "almost" the most serious thing in this case is that a senior official in the Cabinet Office wrote to the police saying that there was "no doubt" that there had been "considerable damage to national security" because of the leaks.
"It was the Cabinet Office, not the Home Office, was the driving force on bringing the police in," he said.
The civil servant who leaked the documents to Green, Chris Galley, was first identified by an internal investigation, "so the whole police involvement was unnecessary".
Committee member Sir Alan Beith asked:
"Did you ever get the impression you were going to be charged under Official Secrets Act?"
Green said it was "clear" from the report into his case carried out by former British Transport Police chief Ian Johnston that in "the early stages there was lots of talk about national security but by the time it came to my questioning there was no discussion" of the Act.
Green was asked, as a possible Home Office minister himself, he approved of leaks.
"All parties benefit from leaks, they reveal serious problems in the department and the responsible attitude for any party is obviously to make it a test about national security or whether it breaks the official secrets act," he replied.
"It would then be an offence to make it public. Nothing that I did could be described like that at all."
He also revealed his House of Commons laptop had been destroyed during the police examination of it.
The Committee on Issue of Privilege relating to Police Searches on the Parliamentary Estate and Internal Processes of the House Administration for Granting Permission for such Action was appointed by Order of the House of Commons in July to investigate the Green case.
Its purpose is to "review the internal processes of the House administration for granting permission to such action, to consider any matter relating to privilege arising from the police operation, and to make recommendations for the future".
