Shadow home secretary Andy Burnham says it may be “impossible” for Labour to reach an agreed position on Trident.
Mr Burnham, who backs renewal of the UK’s nuclear weapons, said a review by shadow defence secretary Emily Thornberry would be “very difficult”.
Jeremy Corbyn backs unilateral nuclear disarmament and Scottish Labour has already adopted such a policy.
But Ms Thornberry has been accused of living in “la la land” amid claims the leadership might “fix” the outcome.
The shadow defence secretary received a hostile reception when she discussed the review at a meeting of Labour MPs on Monday evening. Ex-shadow defence minister Kevan Jones said Ms Thornberry had taken questions “but didn’t answer any”, adding that she had been “waffly and incoherent”.
Some MPs told reporters outside the room that she had said Trident could soon be as obsolete as the Spitfire fighter aircraft was after the Second World War.
Ms Thornberry said she had been trying to explain that Trident may be overtaken by technology such as underwater drones, which were being developed to track submarines.
“The idea of the Trident replacement is that it can hide in the sea. If technology is moving faster than that then it may well be that Trident may not be able to hide.
“And if that’s right, and if we are to bet everything on ‘mutually assured destruction’, we have to be assured that it will work – and if it cannot hide any more then that is a problem.”
She told BBC Radio 4’s Today on Tuesday that “four, five or six people kicked-off” at Monday evening’s meeting of Labour MPs but they did not necessarily represent the whole Parliamentary party.
She said she had wanted to challenge those who had said “it has to be Trident” or nothing.
Asked why she did not just admit that she was against nuclear weapons, she said it was important to discuss all options.
“We need to have all the options on the table and we need to have a proper debate within the party,” she told Today.
Labour peer Admiral Lord West, a former home office minister, telephoned into the Today programme during Ms Thornberry’s interview to say that her argument about underwater drones was “nonsense”.
She said the Chinese, Americans and Russians would not be spending billions on research if there was nothing in it.