Labour MPs reacted angrily after Jeremy Corbyn referred to the party's policy of being in favour of renewing the UK's nuclear deterrent in the past tense.
Mr Corbyn confirmed he will be voting against replacing the UK's current fleet of Vanguard-class submarines which carry the nation's Trident nuclear missiles.
Labour's official policy is to maintain the UK's continuous at-sea deterrence.
Former defence minister Kevan Jones asked Mr Corbyn: "You, like me, stood in May 2015 on a party policy - agreed at our conference through our mechanisms in the party - for the renewal of continuous-at-sea deterrent.
"Now, you have a shadow frontbench and shadow cabinet in your own image which agreed last week, I understand, to put that policy from the frontbench.
"Are you going to do it or is it going to be done in the winding-up?"
Mr Corbyn then replied: "You're well aware of what the policy was." Labour MPs then shouted "is" as Mr Corbyn continued to explain that a review of the policy is being undertaken by shadow defence secretary Clive Lewis.
He added to Mr Jones: "You're also very well aware of the case that I'm making for nuclear disarmament."
Meanwhile, Angela Smith, Labour MP for Penistone and Stocksbridge, intervened and said: "You are very fond of telling us all that party conference is sovereign when it comes to party policy.
"Last year party conference voted overwhelmingly in favour of maintenance of the nuclear deterrent so why aren't we hearing a defence of the Government's motion from the Despatch Box now?"
Mr Corbyn replied: "Party policy is also to review our policies - that is why we have reviews."