London - A furious row in Britain over the police detention of a Conservative member of parliament (MP) Wednesday overshadowed the Queen's Speech - the ceremonial highlight of the parliamentary year.

Amid tumultuous scenes, the Speaker of the House of Commons, Michael Martin, revealed that Scotland Yard anti-terrorism officers had no arrest warrant when they entered parliament last week to search the offices of Damian Green, the opposition Conservatives' spokesman on immigration.

Green was held for nine hours by police while his home and constituency offices were searched, phones cut off and mobile phones confiscated.

The affair, touching on the issue of immunity of members of parliament, and the sensitive question of how freedom of speech is handled in a democratically-elected parliament, has sparked an angry row engulfing both the Labour government and the police.

Prime Minister Gordon Brown Wednesday further angered the Conservatives by refusing to express regret over the police action, and by quoting the police as saying that they were investigating a "substantial series of leaks from the Home Office potentially involving national security."

The queen, 82, who delivered the government's legislative in an elaborate ceremony known as the Queen's Speech, had just left parliament by horse-drawn carriage to return to Buckingham Palace when the row erupted.

Green was detained in connection with the exposure in parliament of a series of alleged immigration policy failures - which were an embarrassment to the government - based on "leaked" information he obtained from a contact in the Home Office (Interior Ministry).

In official legal terms, he was held "on suspicion of conspiring to commit misconduct in a public office and aiding and abetting, counselling or procuring misconduct in a public office."

Green, who spoke in parliament Wednesday, has said it was his "duty" to inform the public about issues such as the employment of thousands of "illegal immigrants" in the security industry or as cleaners in the House of Commons and other institutions.

"The day when exposing facts which ministers would prefer to keep hidden becomes a crime would be a bad day for democracy in this country," Green said.

Home Secretary Jacqui Smith, who has said she was not informed in advance of the police action, is due to make a statement in parliament on the matter Thursday.

Meanwhile, the current acting head of Scotland Yard, Paul Stephenson, Wednesday defended his officers' actions. "The police must be able to act without fear or favour in any investigation," he said.

However, there is widespread speculation that the affair could be a blow to Stephenson's chances to take over as permanent head of Scotland Yard to succeed Ian Blair, who resigned this week.

But it was the revelation by the Speaker that the police did not have a warrant to enter parliament that caused uproar Wednesday.

Martin also said that the police had failed to inform the parliamentary security officer of her right to refuse the police action.

"I was not told that the police did not have a warrant," said Martin to cries of surprise and shouts of "shame."

"From now on a warrant will always be required when a search of a member's office or access to a member's parliamentary papers is sought," said Martin, who insisted that he did not authorize the search.

In the Queen's Speech earlier, the 82-year-old monarch said measures to tackle the economic crisis would be at the heart of the government's legislative programme for the coming year.

"My government's overriding priority is to ensure the stability of the British economy during the global economic downturn," she said.