Jeremy Corbyn is still struggling to draw a line under his reshuffle after three shadow cabinet members refused to rule out quitting if Labour drops its backing for the nuclear deterrent.
The Trident issue is looming as the next major point of contention for the party after the leader shifted Maria Eagle from shadow defence secretary and replaced her with Emily Thornberry, who supports his call for Britain to disarm unilaterally.
The move was widely seen as paving the way for a change in position ahead of a crunch Commons vote - and there are reports Mr Corbyn wants to pass policy-shaping powers from the shadow cabinet to Labour's National Executive Committee (NEC), where his allies have a majority.
A new "consultative process" has also been suggested that could put the final decision on Trident in the hands of the full party membership, which overwhelmingly elected Mr Corbyn.
Under current rules a ballot at party conference would be required to reverse the position, and unions could well block the change for fear of job losses.
Mr Corbyn is likely to be grilled on the issue if he attends the regular meeting this evening of the parliamentary party - the majority of which is thought to be in favour of the nuclear deterrent.
The leader would usually be expected to speak as it is the first gathering after Christmas, but aides said he had yet to decide whether he would.
Asked if he would resign if Labour withdrew support for Trident, shadow work and pensions secretary Owen Smith told Pienaar's Politics on BBC Radio 5 Live: "Well that would be difficult for me but I think the key thing that I would do is stick in, in the run-up to that decision, and make the case.
"We have got to have, I think, a very adult argument in the Labour Party about this - not in public I hope, not in the way in which we have occasionally argued publicly recently - but it is an enormously serious, technical, strategic question for Britain as to what the nature of our nuclear weapons are and whether we have a nuclear deterrent.
"My view is that unfortunately we do need one."
Shadow justice secretary Lord Falconer was asked a similar question on the BBC's Andrew Marr Show.
"Let's see what happens in relation to that but I am clear that I support Trident remaining," he said.
Shadow education secretary Lucy Powell told the BBC's Sunday Politics: "I am not a unilateralist, I think that we should maintain an independent ongoing nuclear deterrent.
"But I am prepared to have a discussion about the capabilities we might need."
Pushed on whether she would resign if the party did officially back scrapping Trident she said: "I would be very surprised if we get to a position where the Labour Party policy is one of unilateral disarmament.
"We will see when we get there, because I don't think we will get there."
Ms Powell said she believed any changes to the party's policymaking process would have to be put to a conference vote.
Meanwhile, shadow Scottish secretary Ian Murray has joined criticism of shadow chancellor John McDonnell for branding the Blairite Progress group a "narrow right-wing clique".
The jibe - delivered during bitter infighting over Mr Corbyn's reshuffle - triggered the resignation of Alison McGovern, who chairs Progress, from a party policy review on child poverty.
Mr Murray, a member of the group, said: "I think some people in the shadow cabinet, including the Shadow Chancellor, should really ramp down the rhetoric a little bit."