Two members of Labour's shadow cabinet have hinted they will quit if the party changes its policy to scrapping Trident.
Owen Smith, the shadow work and pensions secretary, and Lord Falconer, the shadow justice secretary, have both faced questions on whether they would walk away from the front bench over the issue.
The renewal of the UK's nuclear deterrent is looming as the next major point of contention for the party after Jeremy Corbyn shifted pro-Trident Maria Eagle from shadow defence secretary and replaced her with Emily Thornberry, who supports his call for Britain to disarm unilaterally.
Mr Smith was asked on Pienaar's Politics on BBC Radio 5 Live if a shift to a position of unilateral disarmament would prompt his resignation.
He said: "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."
Meanwhile, Lord Falconer was asked a similar question on the BBC's Andrew Marr Show.
He said: "Let's see what happens in relation to that but I am clear that I support Trident remaining."