You face life in prison, Green told

Tory immigration spokesman Damian Green, who will not face criminal charges, said arresting officers told him in November: "Do you realise that this offence could lead to life imprisonment?"

Mr Green was arrested and held by the Metropolitan Police for nine hours on suspicion of "conspiring to commit misconduct in a public office, and aiding and abetting, counselling or procuring misconduct in a public office".

Mr Green told BBC Two's Newsnight that he thought the officer's assertion was "absurd".

The Director of Public Prosecutions said that the leaked information was not damaging enough for charges to be brought against either Mr Green or Christopher Galley, the Home Office civil servant behind the leaks.

Mr Green said of the police: "They said, 'Do you realise that this offence could lead to life imprisonment?'

"I assume it's because it's a common law offence therefore because there is... no law on the statute book which I was alleged to have broken, then presumably there is no set sentence for it. I just thought this was absurd."

Common law is law that has been created and refined by judges through the decisions they have heard in cases over time. This is different to statute law, which is created in Parliament in the form of legislation.

Mr Green said earlier he was "very pleased" with the prosecutors' decision.

He said: "A large part of my job as Conservative immigration spokesman is to expose government failings in immigration policy. That is precisely what I was doing, and that is why ministers were so embarrassed."