Justice Secretary Jack Straw today said that he had been "surprised" at the raid on the Parliamentary office of Tory frontbencher Damian Green.
He said: "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."
Mr Straw, a former Home Secretary and former leader of the House of Commons, indicated that any future review into the raid on Mr Green's parliamentary office was a matter for the House of Commons, but added: "I am pretty certain... that it will be because of the extent of the concern."
Commons leader Harriet Harman said there needed to be an urgent review of procedures to ensure the protection of "big constitutional principles".
Meanwhile, Home Secretary Jacqui Smith insisted officers were investigating a "systematic series of leaks" of potentially sensitive Home Office material. She refused to apologise for the arrest, saying the police had to be allowed to "follow the evidence where they need to" without interference from the Government.
The contrasting positions of Ms Harman and Ms Smith were correct as there were a number of constitutional principles involved, he said.
And he defended Ms Smith's refusal to apologise, claiming there would be a "huge furore" if she did, as it would suggest she was prejudging a police investigation.
It was important that politicians did not "interfere with the natural course of an investigation", he added.
He said competing constitutional principles were in play - the right of MPs being free to carry out "legitimate business" on behalf of their constituents, the independence of the police to investigate and the importance of protecting secrecy and confidentiality "where it is necessary" in Government.
Mr Straw told the Today programme: "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."
He added: "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."