OK, but Tories ordered Trident D5.
Earlier in history labour went for Chevaline, perhaps instead of Poseidon.
And I feel one should credit Churchill with kickstarting Britain's nuclear ambitions. There's a very interesting book on the subject:
Churchill's Bomb. Now, Attlee might be given credit for pushing for development, but I still feel it shows how 'cross-political' major projects are during development.
As an aside I can only think of a single major project that was canned and re-instated by subsequent governments: The B-1 bomber.