No.
No country believes in this religion or that religion; it is an individual choice of the members of that country as to what religion they should believe in (or not).
The lunatic fringe of the far right want to push the notion that the UK (and the USA) is a christian country because they want to use that as an excuse to punish anyone who isn’t. Oh, it’ll start with Muslims and Hindus and end with anyone who doesn’t follow their brand of Christianity.
As of 2021, the UK was 46.5% Christian; that’s the single largest religious group. But it isn’t the majority; there’s plenty of other religious groups and the non-religious. Of course the christofascists will point out that in the past, the UK was nearly 100% Christian, glossing over the fact that this was forced on us – either explicitly or more subtly.
The past is the past – whilst we may have a christian tradition we also have a pre-christian tradition (or a pagan tradition). Christianity is a foreign religion – it’s an immigrant from the middle-east.
