Apologies I haven't read this thread past @piggypigalle who claims that this is a "Christian country".
• For the first time in a census of England and Wales, less than half of the population (46.2%, 27.5 million people) described themselves as “Christian”, a 13.1 percentage point decrease from 59.3% (33.3 million) in 2011; despite this decrease, “Christian” remained the most common response to the religion question.
• “No religion” was the second most common response, increasing by 12.0 percentage points to 37.2% (22.2 million) from 25.2% (14.1 million) in 2011.
From the 2023 ONS. So by my reckoning that means UK isn't predominantly a Christian country.