Police who arrested the Conservative frontbencher Damian Green trawled his private e-mails looking for information on Britain’s leading civil liberties campaigner.

Officers from Scotland Yard’s antiterror squad searched the computer seized from his parliamentary office using the key words “Shami Chakrabarti” – even though the Liberty director had nothing to do with the leaking of Home Office documents that prompted the investigation.

In an interview with The Times, Mr Green warned that his arrest and the raids on his Commons office and homes smacked of a “police state”. The Tory immigration spokesman said that Ms Chakrabarti’s name had been one of the keywords used to go through e-mails and computer documents going back several years.

“This feels to me like a fishing expedition on somebody who embarrasses the government of the day,” he said. “That’s very disturbing.”

The revelation will fuel claims that Mr Green’s arrest, and the police investigation into Home Office leaks, were politically motivated.

Ms Chakrabarti said she had never been approached by the police as part of their inquiry and was alarmed to learn that her name had been used as a key search word. “I think this raises very serious questions about just how politicised, even McCarthyite, this operation was,” she said.

The Government was accused last year of trying to “smear” the Liberty director after Andy Burnham, the Culture Secretary, said that she had “late-night, hand-wringing, heart-melting phone calls” with David Davis, the former Shadow Home Secretary who resigned over the 42-day detention row.

This week the Director of Public Prosecutions, Keir Starmer, threw out the case against Mr Green, who was accused of encouraging a Home Office civil servant, Christopher Galley, to hand over confidential documents. Mr Green said serious questions remained about the handling of the case by the police and the Government. “This was the first time since we became a democracy that an opposition MP had been arrested for political work,” he said. “Arresting opposition politicians is something you associate with police states. We should be very vigilant that we don’t take steps towards that and this was quite a significant step towards it.” Mr Green said he found it surprising that the police had not informed the Home Secretary that they were about to arrest a Shadow frontbencher. “I have spoken to former senior ministers of both parties and everyone says, ‘Of course we would have been told’ ” he said.

Jacqui Smith, who has insisted that she did not know about the arrest in advance, is facing Tory calls to make a statement on the case when Parliament returns after the Easter recess this week. Mr Green stopped short of calling for the Home Secretary to resign but said: “It’s clear that the Home Office is not well run, which in the end is her responsibility.”

Mr Green also criticised Bob Quick, the former head of Scotland Yard’s anti-terrorist squad, saying: “You can’t generalise but there are policemen who have got too close to the Government of the day.”

He was pleased that Mr Quick, who authorised his arrest, had resigned on another matter this month. “I thought that he shouldn’t be in charge of the anti-terror squad because the day they arrested me was the day of the Mumbai bombings. Al-Qaeda might have been trying to do a worldwide spectacular. It did seem to me that to have 25 of the anti-terror squad going through my bank statements and my bed was not what the head of the anti-terror squad should have wanted.”

Mr Green highlighted a series of failings in the police investigation, revealing that officers surrounded the wrong house in his constituency until he took them to his home.

The MP added that it was wrong for the House of Commons authorities to allow the police to search his parliamentary office without a warrant. “There never was and never would be any threat to national security from me,” he said. “If I received information that I thought was a threat to national security, of course I wouldn’t put it in the public domain.”

Police searches of his homes left him feeling as if he had been burgled, he said. Officers rifled through his love letters to his wife and reduced his 15-year-old daughter to tears. His wife, Alicia Collinson, said that the officers had told her that they would have taken a sledgehammer to the door if she hadn’t been at home. “The whole place feels tainted,” she said. “They went through the most personal things. They took photographs as they were working their way through the house. Every so often I find myself doing something and thinking ‘They have pictures of this now.’ ”

She told the Daily Mail that officers leafed through her daughter’s recorder music book. “What on earth they thought they would find . . . It was like being burgled and having to watch.”

Scotland Yard refused to comment last night on Mr Green’s remarks.

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