Jeremy Corbyn has been defied by 20 of his MPs over Trident after they were ordered to stay away from an SNP-inspired debate on scrapping the nuclear deterrent.
Some 14 Labour politicians - including ex-leadership contender Liz Kendall and former shadow chancellor Chris Leslie - voted with the Tories in support of Trident against the SNP opposition day motion.
And six Labour MPs backed the SNP proposal, a position in line with Mr Corbyn's personal thinking but against official Labour policy.
In an effort to avoid confrontation over the controversial policy, Mr Corbyn had ordered MPs not to take part in the vote, which shadow chancellor John McDonnell branded a "stunt".
Labour divisions were plain to see throughout the Commons debate as several pro-nuclear deterrent MPs made pointed speeches in the debate, while shadow defence minister Toby Perkins outlined how support for Trident was current official party policy.
Mr Corbyn, an avowed opponent of nuclear weapons, sparked controversy last week by appointing former London mayor Ken Livingstone as co-convener of Labour's defence review.
The SNP motion was defeated 330 to 64, majority 266.
The Labour MPs who voted against the SNP motion were: Kevin Barron (Rother Valley), Ben Bradshaw (Exeter), Mary Creagh (Wakefield), Chris Evans (Islwyn), Jim Fitzpatrick (Poplar & Limehouse), Ms Kendall (Leicester West), Mr Leslie (Nottingham East), Madeleine Moon (Bridgend), Albert Owen (Ynys Mon), Jamie Reed (Copeland), Emma Reynolds (Wolverhampton North East), Angela Smith (Penistone & Stocksbridge), Gisela Stuart (Birmingham Edgbaston) and John Woodcock (Barrow & Furness).
The six MPs who voted for the motion were: Ronnie Campbell (Blyth Valley), Roger Godsiff (Birmingham Sparkbrook and Small Heath), Kelvin Hopkins (Luton North), Geoffrey Robinson (Coventry North West), Dennis Skinner (Bolsover) and Graham Stringer (Blackley and Broughton).
In the debate, Defence Secretary Michael Fallon said Labour's "shambles" over Trident would provide comfort to Britain's enemies as he appealed to Opposition MPs to renew the political consensus on renewing the nuclear deterrent.
Ms Kendall insisted it is "foolhardy" to oppose Trident on the grounds that Britain does not face a threat from nuclear-armed states at present.
Meanwhile, Mr Woodcock assured the Government that Labour MPs would back Trident renewal.
He said: "I can give you the pledge that Labour MPs will help you get through the programme that we started in government.
"Will you make a pledge in the House today that you will base the Main Gate decision on the operational contracting need of this programme and not on political considerations?"
Mr Fallon replied: "I'm very happy to give you that particular assurance."
Mr Reed said while other nations have nuclear weapons, "so should we", adding it was a clear demonstration of strength and capability which provided Britain's deterrence.
He said: "Unilateralism will never work and believe me, this party has tested that theory to destruction."
Mr Perkins sought to spell out Labour's position on Trident.
He said: "Labour's position, as agreed by the National Policy Forum in 2014 and approved by Labour Party conference in Brighton this year, is that we are committed to a minimum, credible, independent nuclear deterrent delivered through a continuous at-sea deterrent.
"That is the policy that was in the manifesto, that all Labour Party members fought the 2015 general election on and we are proud of the previous Labour government's approach and success in disarmament."
Mr Perkins reiterated that the review is being led by shadow defence secretary Maria Eagle as MPs asked about the involvement of Ken Livingstone.
He added: "It would clearly be ludicrous for me to pretend there aren't differences of opinion within the Parliamentary Labour Party and the wider party on whether this is the right policy."
As one of the supporters of the motion, Mr Godsiff said: "There are usually two arguments put forward as to why the UK should have a so-called independent nuclear deterrent and I have to say in my opinion both of them are myths."
SNP defence spokesman Brendan O'Hara accused Labour of hiding behind "the fig leaf of multilateralism" and said he had no doubt that Mr Corbyn would join the SNP in voting against Trident renewal next year.
He said: "A forlorn hope indeed, but there was a genuine hope that perhaps with the election of Mr Corbyn there would be at least a debate on Trident in this place.
"I fear that the leader has not managed to take his party with him and the paltry attendance today from the Labour Party would suggest exactly that."