Downing Street has today hinted at a review of the procedures that allowed the police to search a Tory frontbencher's office - but not before the current police investigation into Damian Green is over.

Gordon Brown's official spokesman today gave the first detailed rundown on the Prime Minister's attitude to the arrest last Thursday of the Conservative immigration spokesman, and insisted throughout that nothing should be done to undermine an ongoing police investigation.

The spokesman refused to comment on the specifics of the case, but said that that Mr Brown believed important principles had to be considered:

* That the law should not interfere with MPs doing their job.

* That MPs are not above the law.

* That the impartiality of the civil service should not be undermined.

* That the police should have operational independence.

Hinting that Mr Brown accepted Harriet Harman's call for a review he added: "There will be a time when any specific issues arising from this investigation can be discussed. It would not be appropriate to get into a discussion now of the specifics."

Advising caution, the spokesman added: "We do not know the full facts in this case. It is important that we do not rush to judgment. We need to be careful and know what the full facts are."

Asked why an inquiry could not be announced now, he said: "Everybody needs to be very careful about reaching any particular conclusions from this case. There may well be a time when it is right to look at specific issues arising from this case. That is the point Harriet Harman was making but we cannot do that without knowing what the facts are, we cannot do that in a way that would undermine the operational independence of the police in what is an ongoing investigation."

The spokesman confirmed that Mr Brown was aware of the leak inquiry and that a Home Office official had been arrested, but he was not aware than an MP was being investigated.

Earlier, Jack Straw, the Justice Secretary, admitted to being surprised by Mr Green's arrest and said that he understood the concerns expressed by MPs.

He was speaking after it was claimed that detectives accused Mr Green of "grooming" a young civil servant during questioning over the leaking of up to 20 Home Office documents.

Mr Straw defended Jacqui Smith, the Home Secretary, over her refusal to apologise for Mr Green's arrest and the deployment of counter-terrorist officers. He said that in his four years at the Home Office he could not remember a single occasion on which he was informed about the detail of a police investigation, far less invited to comment.

"Everybody who has been made aware of these unfolding events, of course, is surprised by the nature of the raid, and I certainly understand the concern of my parliamentary colleagues," he said.

"If the Home Secretary, any Home Secretary, had offered an apology there would then be a huge furore about the fact the Home Secretary was prejudging the actions and activities of the police without an investigation."

"The Home Secretary is very concerned about this. Of course she understands the significance of a senior Member of Parliament having his offices raided and how unusual this is. It is outside the normal course of events. But anybody who is in the position of Home Secretary, I think, has no option but to take the approach that Jacqui Smith has done."

Ms Smith today repeatedly denied that she knew Mr Green was being investigated. "I did not know the specifics of the investigation," she said.

The Home Secretary added that she would not interfere with the police investigation. "It is a serious issue if a senior politician is arrested. But what I am absolutely clear about is nobody is above the law. Police should carry out their statutory investigation without fear of favour."

Mr Green was held and questioned for nine hours on Thursday "on suspicion of conspiring to commit misconduct in a public office and aiding and abetting, counselling or procuring misconduct in a public office".

His homes and offices, including in the House of Commons, were searched and his computer, phone and other communications equipment seized in the raids, which followed the earlier arrest and then suspension of a junior Home Office official, 26-year-old Christopher Galley.

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