LONDON (AFP) - Prime Minister Tony Blair on Wednesday faced potentially the biggest rebellion from within his own party since the Iraq war as lawmakers vote on renewing Britain's Trident missile nuclear deterrent.
Blair has only been defeated four times in parliament since he came to power in 1997, but a sizeable number of rank-and-file Labour lawmakers have indicated they will go against the government in the early evening vote on the issue.
Although he is unlikely to lose the vote, political commentators say he will have to rely on the support of the main opposition Conservative Party, which critics say will weaken his position.
Outlining his support for renewing Trident last year, Blair told parliament that although the Cold War was over, "new and potentially hazardous threats" to British security from states like Iran and North Korea could emerge.
No other nuclear state in the world was considering unilateral disarmament and it would "unwise and dangerous" for Britain not to have such an "insurance policy" against unspecificed future threats, he said.
Defence Secretary Des Browne, likely to lead the debate in the lower House of Commons, made a direct appeal to Labour rebels Wednesday, telling BBC radio: "We need to take this decision now.
"We need to be clear what this decision means: it's a firm commitment to maintaining our deterrent and that's what I ask members of our party and what I will ask the House of Commons today.
Critics of Trident, including church leaders and unions as well as the traditional anti-nuclear lobby, dispute government claims it would cost 15-20 billion pounds (22-29.1 billion euros, 29-38.5 billion dollars) to replace.
Instead, they argue the figure could rise to more than 100 billion pounds if maintenance and other costs are added, and that the money could be better spent elsewhere.
Opponents say most Britons are against renewing Trident and that in doing so, Britain was being hypocritical because of its attempts to prevent Iran and North Korea obtaining nuclear weapons.
It could also potentially trigger a new wave of nuclear proliferation, they add.
Within Labour, where unilateral nuclear disarmament was once party policy in the 1980s, grassroots members and left-wing traditionalists in parliament have accused Blair of stifling debate on the proposals and want more discussion.
Protests are being held at the Faslane Royal Navy in western Scotland, which houses the four Vanguard-class nuclear submarines that carry the US-built missiles, and outside the Houses of Parliament on Wednesday.
Four Greenpeace protesters scaled a crane on the River Thames next to parliament on Tuesday and plan to stay there until the vote is taken while three protesters scaled the parliament building in Edinburgh Wednesday.
Two junior ministers in Blair's government quit this week to be able to vote against Blair.
More than 100 MPs, including 60 from Labour, have put their names to an amendment to Wednesday's vote aimed at delaying the decision, arguing that the case for renewing Trident is "not yet proven".
The biggest rebellion against Blair was in March 2003 over Iraq, when 138 Labour MPs, including the former foreign secretary Robin Cook, supported an amendment opposing the decision to invade.
Debate on Trident was due to start around 1230 GMT, with a vote scheduled for around 1900 GMT.