Dec. 3 (Bloomberg) -- Until last week, no one in the U.K. had dared search Parliament since 1642, when such an act led to the beheading of King Charles I.

Then on Nov. 27, police investigating government leaks arrested opposition lawmaker Damian Green, 52, raided his parliamentary offices and seized his computers.

“It’s without precedent,” said David Butler, a fellow at Nuffield College, Oxford University. “They were bloody fools to do it.”

The raid has divided Prime Minister Gordon Brown‘s government and triggered calls for the resignation of the speaker of the House of Commons. Some lawmakers plan to complain about it today, overshadowing Queen Elizabeth II‘s annual opening of Parliament -- a ritual intended to remind the monarch of the legislators’ right to resist unwanted interference.

The queen, outlining the government’s legislative agenda for the next year, said lawmakers will consider new banking rules as well as a clampdown on benefit fraud and curbs on immigration. The program is aimed at sheltering consumers from the worst financial crisis in a century.

“My government’s overriding priority is to ensure stability of the British economy during the global economic downturn,” the queen said today from her throne in the House of Lords, the upper chamber of Parliament.

Brown’s Dilemma

The arrest of Green puts Brown in a fix. He has supported the police, saying they must be free of political influence, while insisting he had no prior knowledge of their plans.

“This presents Labour as the party of the secretive state,” said Stephen Driver of Roehampton University. “It plays very well for the Conservatives, allowing them to be on everyman’s side against big government.”

Green’s arrest highlights tension rooted in Britain’s unwritten constitution, which has evolved for a thousand years. Although Parliament is a palace owned by the crown, the monarch has been barred from the House of Commons since the 1642 incident. Today she addressed lawmakers of both chambers from her throne in the upper House of Lords.

Civil War Spark

The episode almost four centuries ago began when Charles I entered the chamber with soldiers to search for five lawmakers who resisted his claim of a divine right to rule. Speaker of the House William Lenthall refused the king’s demand to identify the lawmakers so they could be arrested.

In the ensuing civil war, Parliament’s supporters defeated the king’s. A plaque in Westminster Hall in Parliament marks the spot where Charles was tried before his 1649 execution. To this day, lawmakers pledge loyalty to the Queen while upholding their right to challenge the government.

Green had embarrassed the Home Office -- which oversees police and immigration matters -- by publicizing confidential documents showing that a recession would lead to a rise in crime and that it had cleared 5,000 illegal immigrants to work as private guards and one to work as a Parliament janitor.

Police held Green, the Conservative Party‘s immigration spokesman, for nine hours. They searched his offices and homes in London and Kent in Southeast England, confiscating his mobile phone, Blackberry and computers. A police statement said they were investigating whether Green was conspiring to “commit misconduct in a public office” by encouraging leaks.

Green’s Arrest

After being released, Green said he was “astonished” to have been held “for doing my job.”

Paul Stephenson, acting commissioner of the Metropolitan Police, told London Assembly members today that his force had been called in by the government because of potential national security risks.

Stephenson said his officers had written permission from the Sergeant at Arms Jill Pay, who oversees day-to-day security in Parliament. She reports to Speaker of the House Michael Martin, who has ultimate responsibility for the matter.

Today, Martin said Pay authorized the raid but wasn’t informed she could ask for a warrant, which the police had not drawn up. He said he would name a panel of seven senior lawmakers to look into the matter and allow a House of Commons debate on the issue next week.

“If there was a threat to national security, it is right for the police to investigate and for them to take action,” George Foulkes, a Labour member of the House of Lords, told BBC Radio 4 earlier. Replying, David Davis, Green’s former boss, said the suggestion was “entirely ludicrous.”

“Had there been a national security issue here, the Official Secrets Act would have been the law under which they carried out both arrests,” Davis said. “You wouldn’t have heard a word from anybody until it was concluded.”

Conservative Informant

Green and his informant, 26-year-old Home Office employee Christopher Galley, were arrested over suspected “misconduct in a public office.”

Business Secretary Peter Mandelson told the BBC today the Conservative outrage was a “smokescreen” to obscure their relationship with Galley, who “in an attempt to pursue his political ambitions in the Conservative Party allegedly systematically passed sensitive and classified Home Office papers to the Conservative Party, apparently in the full knowledge of the Conservative front bench.”

A similar contretemps erupted in the U.S. in 2006, when authorities searched the congressional office of Representative William Jefferson during a probe that led to the Louisiana Democrat’s indictment on bribery charges. He denies wrongdoing and probably will be tried next year.

Unlike British lawmakers, who mostly rely on precedents to defend against overreaching by police, members of Congress enjoy protection from Article I of the Constitution, a legacy of the struggle for independence from Britain.

American Protections

The Constitution protects American lawmakers from arrest in some circumstances and says “they shall not be questioned in any other Place” for “any Speech or Debate in either House.”

Members of Congress from both parties said the Jefferson search violated that clause. A federal appeals court later ruled that the investigators had stepped over the line and ordered them to return some documents to Jefferson.

“A lot of people who don’t like him were still outraged,” said Thomas Patterson, a professor of government at Harvard University’s Kennedy School of Government in Cambridge, Massachusetts. Given the U.K.’s history, “it’s surprising that something like that could happen in Britain.”

The fact that Britain’s constitution is unwritten muddies the questions surrounding Green’s arrest. The only written guarantee U.K. lawmakers enjoy is that they can’t be made to answer for their words in Parliament in any court, effectively protecting them from libel cases.

Cabinet Split

Brown’s Cabinet ministers have split on the issue. Home Secretary Jacqui Smith backed police and said it would be wrong for her to prevent such an investigation. Harriet Harman, deputy Labour leader, said she wants to ensure that “big constitutional principles” are protected.

Brown yesterday signaled support for the police, saying “no member of Parliament is above the law.” The day before, his spokesman Michael Ellam said Brown also believed that “important principles” needed consideration.

In deeper jeopardy is Martin, the Labour lawmaker who is speaker of the House. In olden times, that position was often unpopular because it involved conveying messages to monarchs, who had seven speakers beheaded. Like all newly elected speakers, Martin was ceremonially dragged to his chair when he took the post in 2000.

“If he let the police raid a member of Parliament’s offices for doing his job and holding the executive to account, I’m not sure he can remain speaker,” said Conservative lawmaker Douglas Carswell.

Speaker’s Jeopardy

In today’s ceremony, a representative of the queen marched through the central lobby of Parliament and summoned the House of Commons to hear the monarch. They slammed the door in his face, signaling their independence.

“Any Tory moles at the Palace?” asked Labour’s Dennis Skinner to laughter in the House of Commons as the queen’s representative summoned lawmakers.

In another ceremonial reminder of the tension between the crown and Parliament, a junior lawmaker in the government, this year Claire Ward, was kept hostage at Buckingham Palace while the Queen is in Westminster, and only released on the monarch’s safe return.

Filing into the House of Lords, lawmakers passed a mural depicting Speaker Lenthall refusing Charles I. Technology has moved on since then. Yesterday, the Conservative’s Web site featured video of the police raid of Green’s office.

To contact the reporter on this story: Robert Hutton in London at rhutton1@bloomberg.net

Last Updated: December 3, 2008 10:09 EST