Commons speaker Michael Martin was heading for a showdown with his Westminster critics last night as fellow Scottish MPs claimed he is the target of a witchhunt over the arrest of Conservative MP Damian Green.

Commons speaker Michael Martin was heading for a showdown with his Westminster critics last night as fellow Scottish MPs claimed he is the target of a witchhunt over the arrest of Conservative MP Damian Green.

The Conservatives have angrily accused Mr Martin of causing a breach of parliamentary privilege by allowing police officers to raid Mr Green's Westminster office, and are using the issue to launch another attack on the Speaker.

MPs on both sides of the House regard the police operation within Westminster as a breach of parliamentary privilege and have called for Mr Martin to explain why the Metropolitan Police were allowed into the palace.

Last night, the Conservatives added fuel to the fire by releasing still photographs on their website of police searching Mr Green's Westminster office.

Mr Martin has been the target of a long campaign by elements of the Conservative party since he took office in 2000. He will face his critics at 2.30pm today after the most auspicious event in the Westminister calendar, the state opening of parliament by the Queen.

Yesterday, the Metropolitan Police sought to defuse the growing controversy over its inquiry into leaks from the Home Office by establishing an urgent review by the chief constable of another force.

The Met's Acting Commissioner, Sir Paul Stephenson, called in the head of the British Transport Police Ian Johnston to look into his force's "decisions, actions and handling of the investigation", Scotland Yard revealed. An interim report from Mr Johnston is expected within seven days, with a full report the following week.

Prime Minister Gordon Brown also indicated that there may be further inquiries after the conclusion of the investigation, which saw the arrest of Mr Green on suspicion of conspiring to commit misconduct in a public office. The Ashford MP, who denies all wrongdoing, has been bailed until February.

Mr Brown told reporters: "MPs have got to be allowed to get on with their job, but no MP is above the law. The police have got to be able to get on with their job without interference by politicians."

In a day of angry exchanges across the political divide, the Home Secretary Jacqui Smith welcomed Mr Johnston's review and restated her support for the police's operational independence.

Ms Smith further angered Tories by meeting representatives of the Commons authorities and Leader of the House Harriet Harman to discuss arrangements for today's statement by Mr Martin.

Senior Tories including former home secretary Kenneth Clarke and ex-shadow home secretary David Davis are expected to lead demands for a full debate today, which may delay the scheduled debate on the government's legislative programme.

Some Tory MPs are considering tabling a motion of no confidence in the Speaker, which could pave the way for his removal. Harwich MP Douglas Carswell said he was not alone in thinking Mr Martin was "not up to the job".

Last night, Jim Sheridan, the Labour MP for Paisley and Renfrewshire North, came to Mr Martin's defence, saying that he was the victim of a political witchhunt. "The Tory establishment has tried to undermine the Speaker from day one simply because of his background. I'm concerned about the fact that he has been unable to defend himself. They have undermined the whole principle of how someone is innocent until proven guilty."

The back bencher, who chairs the Labour Group of Scottish MPs, added that people should wait on passing judgment until after the Speaker has made his Commons statement today and that, if a satisfactory explanation is given, Conservative MPs should then apologise.


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