Well, here are some figures from the last UK census, where we ask such questions:
It reports about 25% have no belief.
While Christianity is the major religion, many will put that down on the form when they really only ever go to church to be hatched, matched or dispatched.
Politicians generally keep religion out of polticial conversation, even if they have strong beliefs. Tony Blair, for instance is, I believe quite a devout Catholic, but in office, he kept quiet about it. His PR man Alistair Campbell, famously said of religion and politics: ‘We don’t do God’. The reason for this is that it would not go down well with the voters who regard religious piety as a personal thing, not something you wear on your cuff.
There are deeply religious people in the UK, this is most evident in immigrant communities from the West Indies and Africa and the Muslim and Hindus from India and Pakistan, where is a strong element of community life. They have more issues with each other than rest of the population.
There are one or two areas of the UK where Christianity does becocme poltiical and that is in Northern Ireland and parts of Scotland, where you get the last echoes of the Reformation and they have a sad history of sectrarian politics where being Catholic or Protestant marked you down as being automatically belonging to one political camp or another. Thankfully, that Constitutional problem is largely a thing of the past.
I the rest of Europe, it is pretty much the same except for countries like Ireland and Poland where Catholicism played an important political role. European history is littered with hideous religious conflicts and the many constitutions that were written after WW2 took care to put in clauses to guarantee religious freedom, just like the US.
The social trend in most countries is that religious belief matters less and less. The past decades have seen marked reductions in church attendance, in the UK it is about 6%. I am not sure why this is.
Though the UK, with its official protestant Church of England, still has seats in the second chamber of Parliament reserved for Bishops. Things don’t change very quickly around here.
With respect to Atheism, we have a few militant Atheists like Richard Dawkins who like to provoke a debate with bishops and are the scourge of the intelligent design people (if you can find any.) However, it is a rarified intellectual argument rather than a popular one. No-one is going to get too upset by it.
Rather than belief or non-belief in religious terms, people seem to contrive their own set of beliefs from different sources. One wry commentator observed that if the UK has one unifying religion it is the belief in the sanctity National Health Service and virtue of public service for the common good.
A bit different from the US, I think.