The US and Nazi China have already been in world war 3 since the Korean war. It remains to be seen how much longer we can last in it but it's not looking very good.
That's true, but the UK is barely a power at all.
The US spends more[1] and has greater production capacity[2] than any other country ever has. If it is not a superpower, then what is it?
[1]: https://en.wikipedia.org/wiki/List_of_countries_by_military_...
[2]: https://web.stanford.edu/class/e297a/U.S.%20Defense%20Indust...
The current government in the UK was more aligned to the worldviews of Trump's administration. They'll throw shade at the current US administration whenever and wherever they can in an attempt to bolster their own standing which has taken strain. The British public follow US politics very closely.