In effect, all Corbyn has done is neuter the Deterrent should the UK public take leave of their senses and elect him as PM. Assuming he doesn't then immediately scrap it, his "Letters of Last Resort" could merely say "don't fire under any circumstances"; that way the unions are happy as the boats will be designed, built and maintained and the ghosts of the CND nut jobs can be happy about us not incinerating those that have already incinerated us, with no regard to civilian casualties....He can also, legitimately, change his mind (unlikely I know...he still seems to rate Diane Abbott...). It also enables Labour to campaign on a non-unilateralist stage, albeit with strong caveats, and would permit future govts the choice to behave differently. However, "Choice" appears to be an anathema to Corbyn and Cronies who prefer to dictate behaviours/beliefs from a smug position of pseudo-intellectual superiority - as indeed do most Left Wing regimes.