A difference over the retention of Britain's Trident nuclear deterrent last night caused the first major rift between the two rivals bidding for the Liberal Democrat crown.

Chris Huhne, the party's environment spokesman who launched his leadership manifesto yesterday, spelled out his opposition to Trident, insisting the LibDems should say now that they would not replace it. He said: "You cannot properly equip our soldiers and spend £20bn on replacing Trident. We must back our troops and not Trident."

However, Nick Clegg took a different tack, arguing that such a move would destroy the UK's bargaining power in non-proliferation negotiations in 2010.

In an article for the grassroots internet blog LibDem Voice, the party's home affairs spokesman wrote: "There's little point attending the talks if we've already thrown all our cards away. As Geoffrey Howe once said - it's like sending your batsmen into the crease with broken cricket bats."

As leadership nominations closed yesterday evening with just two hats in the ring, it emerged the party had signed up around 2000 new members since Sir Menzies Campbell quit just more than a fortnight ago. At least 64,000 members will receive ballot papers when they are sent out on November 21, although the party is expecting numbers to swell further as the leadership contest gathers pace. The new leader will be announced the week before Christmas.

At his manifesto launch, Mr Huhne pledged to give the public a referendum on new laws if enough people were opposed within a period of at most 100 days of its passage through the Westminster Parliament.

"We need a people's veto to block unwanted law," he said, arguing that it would introduce a new check on the "overweening" powers of the executive. Mr Huhne, 53, the MP for Eastleigh in Hampshire, suggested that the number of voters required to trigger a referendum should be 2.5% of the population.

The underdog candidate, who unsuccessfully challenged Sir Menzies for the party leadership in 2006 following the resignation of Charles Kennedy, also matched a promise by Mr Clegg to lead a campaign of mass civil disobedience against identity cards if they were made compulsory.

Before of Mr Huhne's manifesto launch, Mr Clegg, 40, who represents Sheffield Hallam, announced he was prepared to risk being hauled up in court over his opposition to ID cards.

He said he would lead a "people's campaign" against the controversial ID cards programme and refuse to take part. "I, and I expect thousands of people like me, will refuse to be forced to register. This is an issue that is so contrary to the spirit of British liberty and privacy that I would not be able to stand by." He added: "I am willing to do everything in my power to stop this intrusive, expensive and unnecessary imposition on the liberty of the British people."

Out of the party's 63 MPs, 32 MPs have come out for Mr Clegg compared to just 10 who are supporting Mr Huhne.

The contenders
Nick Clegg
Age: 40.
Educated: Westminster School; Cambridge University.
Status: married with two sons.
Work: journalist; political consultant; European Commission official; lecturer.
Politics: MEP; MP since 2005; home affairs spokesman.
Appeal: photogenic, media-savvy, seen as on liberal economic wing, capable of wooing wavering Tories.
Odds: 1/3.

Chris Huhne
Age: 53.
Educated: Westminster School; Oxford University.
Status: married, one daughter, two sons, two stepdaughters.
Work: journalist; economist.
Politics: MEP; MP since 2005; environment spokesman.
Appeal: intelligent, economically grounded, experienced, regarded to left of his rival, having campaigned previously he has done much of the grassroots legwork.
Odds: 9/4.