Justice Secretary Jack Straw has appeared to indicate that ministers had been "surprised" by the nature of the raids on Tory frontbencher Damian Green's homes and offices.

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 Speaker Michael Martin is under mounting pressure from MPs to explain why police were allowed to raid the Parliamentary office of Mr Green.

Amid speculation that anger could erupt into protest, the Speaker's office announced that Mr Martin would make a statement on Wednesday when the House returned for the State Opening of the new session.

Politicians from all sides have condemned the police action - former Labour minister Denis MacShane dubbed it "a mammoth breach in the core democratic doctrine of parliamentary privilege".

Commons leader Harriet Harman told Mr Martin there needed to be an urgent review of procedures to ensure the protection of "big constitutional principles".

Home Secretary Jacqui Smith has refused to apologise for Mr Green's arrest and has denied he was being pursued simply for doing his job of holding the Government to account. She said on Sunday that police were investigating a "systematic series of leaks" of potentially sensitive Home Office material.

Mr Straw, who was with Ms Smith in Slough, acknowledged that the Green case raised issues about police ability to enter Parliament.

"There are plainly issues about access to Parliament that I am sure some people will deal with," he told reporters.