Well there was a step change in '53 with Joe 4 which was a Russian 400Kt H-Bomb.
And there was a step change four years later in 1957 with Grapple.
You're assuming they'd all reach their targets, would not blow up accidentally and that they would actually detonate when they reached their targets.
Which might equally apply to the Soviet nuclear weapons.
There is no way on Earth that the UK could ever single handedly match the nuclear production capabilities of either the US or the USSR
True - but we didn't have to. All we had to do was to make enough bombs to deter the Soviets from attacking.
We didn't need to compete. After all, the UK could be taken out with a few dozen bombs. Anything else would be just re-arranging the rubble.
As for Macmillan's 'great prize' - in the end, it turned out to be overrated. We didn't need the US designs - we had working ones of our own. The major difference was that ours were not 'weaponised', and to do that we would needed to have done more tests at a time when atmospheric testing was very unpopular.