I have to wonder why. I would expect that the technology and mitigations are fundamentally the same. Perhaps the difference is cultural.
US population is ~5x greater than the UK, while UK GDP per capita is less than the US. More generally, the per capita economic posture of the US is strong compared to the top 10 most populous countries in the world. If you were an opportunist robocalling scammer operating on a purely probabilistic model, the UK would be a pragmatically irrelevant target. The situation in the US isn't helped by regulatory capture either.