On the day of the Queen's Speech, the Speaker of the House of Commons usually plays a small role in setting the ceremonial scene. But today he will be centre stage. For after the Queen has spoken and the champagne has been quaffed, Michael Martin has some explaining to do. The Speaker must explain his role in the almost unprecedented entry of police officers into the Palace of Westminster last Thursday, and in the arrest and wholly disproportionate treatment of the MP Damian Green.

Mr Martin needs to reveal whether or not he authorised anti-terrorist officers to enter the Palace of Westminster, and on what basis they were admitted. He needs to say what role was played by his Serjeant at Arms and the Clerk of the Commons; and why his office appears to have acted with such cavalier disregard for parliamentary privilege. MPs should not be above the law. But they should also expect to carry out their duties - one of which is to hold governments to account - without undue interference. There is no suggestion that Mr Green broke the Official Secrets Act, only that he leaked information about immigration policy that was potentially embarrassing to the Home Office. To allow police to search his parliamentary office, seize his computer and disable his e-mail account was an assault on parliamentary privilege. The Speaker must explain either why he authorised it, or why his office did not inform him.

There has been an alarming abrogation of responsibility in this case by people who should have known better. Yesterday the Home Secretary welcomed the news that a senior police officer will investigate Scotland Yard's handling of the investigation into Home Office leaks. She asked that it be pursued “diligently, sensitively and in a proportionate manner”. She should have asked those questions about the initial police operation. Even if she was not informed that an MP was about to be arrested - and she ought to have been - she should have appreciated the gravity of the situation much earlier.

The heavy-handed style of the police investigation has exacerbated matters. Mr Green has not endangered the security of the nation. The invasion of his house by counter-terrorist officers was absurd. His interrogation for nine hours was excessive. The presumption behind raids of this kind is that the suspect may destroy evidence. The presumption behind a surprise, heavy-handed arrest is that the suspect will resist. Both ideas are laughable. Mr Green is not a Mafia boss. A summons, a warrant or a simple invitation would have served perfectly well to get his co-operation.

The haughty way in which the conduct of legitimate parliamentary activities was confused with terrorist ones poses serious questions about the use the police will make of their new counter-terrorist powers. A ministerial shrug is a grossly inadequate response. It is a symptom of tired government that people fail to ask themselves whether they should take responsibility, preferring to hide behind bureaucratic procedures. Neither the Speaker, nor the Home Secretary, nor the Prime Minister, appear to have understood the fundamental issues of liberty raised by the actions against Mr Green.

The Leader of the Commons sees things differently. Harriet Harman has made clear her determination to investigate the processes that led the Commons authorities to allow the police to search Mr Green's office at the House. In the past, Ms Harman has also been accused of receiving Home Office leaks. She knows that holding the Government to account is an honourable practice. If the Speaker is unable or unwilling to fulfil his constitutional role in protecting that practice, he should consider his position.