Senior Tories have reacted with fury after a front-bencher was arrested by anti-terror police.

Conservative immigration spokesman Damian Green, 52, was held at Belgravia police station in central London on suspicion of leaking confidential Home Office papers to the media.

He "emphatically" denied any wrongdoing, saying: "I was astonished to have spent more than nine hours under arrest for doing my job."

"I have many times made public information that the Government wanted to keep secret - information that the public has a right to know.

"In a democracy, opposition politicians have a duty to hold the Government to account. I was elected to the House of Commons precisely to do that and I certainly intend to continue doing so."

Senior Tory sources described the operation as "Stalinesque" and suggested police must have received authorisation from the very top of the Government.

Tory leader David Cameron said: "I think there are some serious questions that have to be answered. If they wanted to talk to Damian Green, why not pick up the telephone and ask to talk to him?

He said it was a "worrying stage in our democracy" where shadow ministers could not release information in the national interest, adding: "If this had happened in the 1930s, Churchill would have been arrested."

Mayor of London Boris Johnson revealed that he was informed of police plans in advance and voiced "grave" concerns to acting Met Commissioner Sir Paul Stephenson, warning him that he did not regard it as "common sense policing".

He said he found it "hard to believe that on the day when terrorists have gone on the rampage in India that anti-terror police in Britain have apparently targeted an elected representative of Parliament for no greater crime than allegedly receiving leaked documents".

Downing Street and Labour issued strong denials that either Prime Minister Gordon Brown or other ministers had prior knowledge.

The Metropolitan Police Service released a statement saying "the decision to make today's arrest was taken solely by the Metropolitan Polce Service without any ministerial knowledge or approval".

Mr Green was released on unconditional bail without charge, but must return to face further questioning in February.

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