Green arrest: MPs demand answers

The frontbench MP was held for nine hours on Thursday and his offices and homes searched over his alleged involvement in the leak of information from the Home Office.

A detailed series of questions has been put to ministers by the Opposition about who knew in advance about what party leader David Cameron denounced as "heavy-handed" tactics.

Gordon Brown and Home Secretary Jacqui Smith have both insisted that ministers were not involved in any way in the decision to arrest Mr Green and that it was purely a matter for the police.

Much of the anger is being directed towards Speaker Michael Martin and the House of Commons authorities for allowing police into the Palace of Westminster to search Mr Green's Commons office.

Asked if Mr Martin had approved the move, a spokeswoman issued a terse statement, saying simply that: "There is a process to be followed and that was followed."

However, the Home Office confirmed that the police would have required permission from House authorities to carry out a search on the Commons premises.

Tory backbencher Douglas Carswell said that if it was confirmed that Mr Martin had authorised the raid, which some say breached Parliamentary privilege, he would be demanding his resignation.

"The purpose of the Commons Speaker is to preside over an institution that holds government to account - not to give the green light to police raids against legitimate opposition," he wrote on his internet blog.

The arrest has caused alarm and disquiet across Westminster, with Liberal Democrat leader Nick Clegg dubbing it "something you might expect from a tin-pot dictatorship" and veteran Labour former cabinet minister Tony Benn complaining of a "direct attack on Parliamentary democracy by the police".