ColinB: Was it really worth such a price. You have placed this Q in its correct historical context, not from hindsight or from a CND stand. Proper Q.
Truman, mantle of FDR and aware of the wider world, was going to lose Nov.48 Election to isolationist trade barons (see the photo of a paper's headline early on the night, saying he had, held up by a grinning, surprised HST). We liked the Asst.SecState, Dean Acheson (the fellow just as urbane as Eden), but he, too, knew his lot would lose and returned to his law firm in 1947. So, just us, then v.Uncle Joe and his shenanigans. We thought he would have the Bomb by about 1955, so Attlee accepted so too must we, after HST signed on to the MacMahon Act, August,1946, which denied us access to "our" Bomb. Sir W.Penney put his team together from May,1947 - it included his Manhattan colleague, K.Fuchs, Stalin's man.
Ike chose to rescind MacMahon as affecting UK in 1957, and thereafter UK carried loan or adapted US stores. The Official position is that we had earned the right to that special treatment, and on to Joint Target Policy Committees, because we had got stuck in, solo, spending heavily in recognition of the common Threat. Hard, I suggest, for us quiet perusers to gainsay that judgement. It's really not open to proof, for, or against. Staying in the business through 2 generations of SSBN, and now talking of a third, is more of the same: the savings we would take from exit are (merely a few) £billions, and aren't we now blase about those numbers; the risk is of cold draughts if we found ourselves at High Noon, all alone. France, also denied by MacMahon access to Joliot/Curies' Bomb, did it all near-solo, so even more expensively as a GDP %, for the same reason. She chose not to be SIOP-integrated, but to point a tous azimuts. The Bomb is like the wife: hard to live with, harder without.