June 11 (Bloomberg) -- Prime Minister Gordon Brown survived a rebellion in the U.K. Parliament over his plan to increase the length of time police can hold terrorism suspects without charge to 42 days after a rival party backed the government.

Members of Parliament voted 315-306 to extend the detention period from the current 28 days. Thirty-six lawmakers from the ruling Labour Party voted against the plan, enough to defeat it in the House of Commons. The Democratic Unionist Party's nine lawmakers voted with the government.

The nine-vote margin of victory leaves the bill vulnerable to amendment in the House of Lords, the upper chamber of Parliament that will begin considering the measures as soon as tomorrow. It also leaves questions in place about Brown's ability to manage the government and his party.

``I'm not sure how much good this victory is going to do him,' Bill Jones, a lecturer in politics at the University of Manchester, said in an interview. ``The only victory lies in avoiding a defeat.''

Brown will hold a press conference at 10:30 a.m. in London tomorrow. The House of Commons finishes work on the legislation today. No party holds a majority in the House of Lords, which must agree with the rules before they can become law.

`Worst Possible Result'

``This is the worst possible result for the government,'' John Grogan, a Labour lawmaker who voted against the plan, said on Sky News after the vote. ``The problem now for the government is this has got to go to the House of Lords. The Lords are going to savage this legislation.''

Brown's popularity with voters has plummeted since he took over from Tony Blair a year ago as the economic slowdown deepened, leading to questions about whether he can continue to lead Labour into the next election, due by the middle of 2010. Labour trails behind the Conservative Party by 20 percentage points in opinion polls.

``I was going to vote initially against the government,'' Labour lawmaker Austin Mitchell said on Sky News. ``Finally at the end I was persuaded to vote with the government to save Gordon for the nation. He would be on his way out if he were defeated on this.''

Last month, Labour was trounced in local council elections and lost a parliamentary seat to the Conservatives it had held since World War II. A defeat today may have further undermined Brown's authority.

Government Argument

Ministers argue the increasing complexity of terrorism cases mean the police need longer to examine them. They have cited an alleged 2006 plot to bomb airliners as proof of the case for extra time, saying investigating officers were close to releasing the suspects because of the 28-day limit.

``We cannot simply hope for the best,'' Home Secretary Jacqui Smith said in Parliament. ``We must have plans in place to cope with the worst.''

Brown says the security services are currently investigating 30 potential terrorist plots, 2,000 terrorist suspects and 200 networks. In recent cases, police needed to examine 400 separate computers, 8,000 discs and 25,000 exhibits, he says.

``We should be facing up to an issue of public security,'' Brown told lawmakers before the vote. ``The government must make a judgment, and the judgment is not that it is popular, but that it's right and necessary for the security of our country.''

Britain's detention limit compares with one day in Canada, two in the U.S. and Germany, four in Italy, five in Russia, and six in France, according to Liberty.

Conservative View

The Conservatives say that if elected they would reverse any extension. Brown must hold an election by mid-2010 at the latest. The Counter Terrorism Bill may also face opposition in the upper House of Lords when it passes the lower chamber.

``We won the argument, the government bought the votes,'' David Davis, a Conservative lawmaker who speaks on law and order. ``Ministers utterly failed to provide the evidence in favor of 42 days in the Commons, and the measure is likely to be rejected in the House of Lords.''

Blair suffered his first parliamentary defeat in 2005 when lawmakers rejected an attempt to raise the pre-charge detention limit to 90 days from 14. He sought the increase after four suicide bombers killed 56 people, including themselves, on London's public transport network.

Without DUP support, the vote today would have been a tie, forcing the speaker of the House of Commons to use his casting vote. Nigel Dodds, deputy leader of the DUP, said his lawmakers voted with the government because of national security concerns.

``We have decided to vote for the extension of the pre-charge detention period after careful consideration of all the arguments,'' Dodds said in an e-mailed statement. ``We believe, on balance, that this change in legislation is right and is in the best interests of national security in the United Kingdom.''

To contact the reporters on this story: Kitty Donaldson in London at kdonaldson1@bloomberg.net; Robert Hutton in London at rhutton1@bloomberg.net

Last Updated: June 11, 2008 14:29 EDT