Effects on early Cold War? Korean War? Would US be willing to use nukes in Korea if they didn't have to feature in Soviet arsenal?
Ok, we get a (mega)ton of "US nuke delayed" but what about if Soviet one is delayed for a few years? Some spies are caught, some Soviet scientists die.....
If you could stretch it out to three that could possibly make the UK the world's second nuclear power. Don't think it would cause any major changes, other than giving the British government a bit of a confidence boost about still being a great power, but it amused me....if it's just a year or two I don't know if it would make that much difference in the long run.