David Cameron was last night standing by his immigration spokesman after Damian Green was arrested by Scotland Yard on suspicion of being involved in leaking UK Government information.

David Cameron was last night standing by his immigration spokesman after Damian Green was arrested by Scotland Yard on suspicion of being involved in leaking UK Government information.

The Conservative leader was said to be "very angry" at the way the case had been handled - counter-terrorist police were thought to have been involved - but "supportive" of Mr Green, who has not been charged with any offence and denies any wrongdoing.

The 52-year-old MP for Ashford in Kent was arrested yesterday at his constituency home and taken to a London police station. He was later released on bail to return for further questioning in February.

It is understood the arrest was in connection with allegedly leaked information relating to stories which have appeared recently in the media.

The allegations are thought to centre on four stories which have caused embarrassment to the government, including the fact an illegal immigrant had been employed as a cleaner in the House of Commons, which emerged in February this year, and a letter from Home Secretary Jacqui Smith to Prime Minister Gordon Brown warning that the recession could lead to a rise in violent crime and burglaries.

It is understood Mr Green's arrest stems from an investigation into a Home Office official who was arrested last week. That arrest resulted from a molehunt initiated by senior civil servants in the department, who later called in police. Questioned about Mr Green's arrest, a Home Office spokesman said: "We can confirm that a Home Office official was arrested last week in connection with an inquiry into alleged leaked documents."

Shadow chancellor George Osborne on BBC1's Question Time said: "I think it is absolutely extraordinary that the police have taken that decision. It has long been the case in our democracy that Members of Parliament have received information from civil servants. I think to hide information from the public is wrong. It is very early days. It's an extraordinary case. I think there are going to be some very, very big questions asked of the police."

A spokesman for 10 Downing Street said: "The Prime Minister had no prior knowledge of the arrest of Mr Green and was only informed after the event."

In a statement, the Conservative Party said: "As shadow immigration minister, Mr Green has, on a number of occasions, legitimately revealed information which the Home Office chose not to make public. Mr Green denies any wrongdoing and stands by his actions."

Without naming Mr Green, the Met said: "The man has been arrested on suspicion of conspiring to commit misconduct in a public office and aiding and abetting, counselling or procuring misconduct in a public office."

Later, speaking to reporters outside the House of Commons at around 12.45am today, Mr Green said: "I was astonished to have spent more than nine hours today under arrest for doing my job. "I emphatically deny I have done anything wrong."