Britain's House of Lords voted Monday against a controversial plan to extend the amount of time police can hold terrorism suspects without charge from 28 to 42 days while an investigation is conducted.

Members of the House of Lords rejected the proposals by 309 votes to 118 after an impassioned debate, dealing the government a significant defeat.

Home Secretary Jacqui Smith will make an emergency statement on the bill to the House of Commons later Monday evening.

The government says the proposal — endorsed by the House of Commons in June by a margin of only nine votes — is needed to fight the complex international terrorist threats facing Britain.

But a number of prominent politicians, writers and the Council of Europe have attacked the plan as a threat to civil liberties. The council, Europe's top human rights watchdog, said the plan would imperil the right to a fair trial.

Baroness Eliza Manningham-Buller, a member of the House of Lords who used to head the domestic spy agency MI5, condemned the measure as unnecessary and said it could jeopardize Britain's freedoms.

"I have weighed up the balance between the right to life — the most important civil liberty — the fact that there is no such thing as complete security, and the importance of our hard-won civil liberties," the former spy chief said. "On a matter of principle, I cannot support 42 days pre-charge detention."

The current MI5 director stayed neutral on the issue, saying it was a police matter.

The issue has divided Britons in the years since the Sept. 11 attacks raised fears of terrorism. At the time, there was a two-day limit on detention without charge, which could be increased to seven days with court permission.

The government's effort to strengthen counterterrorism provisions gathered pace after suicide bombers killed 52 rush-hour commuters in London in July 2005.

Still, then-Prime Minister Tony Blair suffered his first major defeat in the House of Commons later that year when he tried to extend the limit to 90 days. Eventually, a 28-day limit was enacted — the longest detention period in 15 Western democracies studied by the British rights group Liberty, according to spokeswoman Jen Corlew.

Brown and Blair have maintained that extra time is needed to build cases against terrorism suspects because of their extensive contacts overseas and their use of multiple computers.

Andy Hayman, a former police officer who headed London's counterterrorism operations until last year, has said an extension of the detention time allowed before charges are brought is needed to tackle increasingly complex terrorism cases.

Opponents of the 42-day measure note that there have not been any cases when 28 days were needed to evaluate a terrorism suspect, and say this shows that the extension to 42 days is unnecessary.

The effort to stop the proposal received a boost this weekend when 42 prominent British writers banded together to denounce the plan as antidemocratic in essays, stories and satires.

Author Linda Grant wrote that the proposal undermines British principles of fair play.

"The nature of democracy and of basic human liberty rests on the fact that you can't be imprisoned unless you have been charged with a crime and convicted of it in the courts," Grant said in her essay. "The courts remain the places where justice is tested — if you have a case, make a charge."