Christian Focus are a really nice bunch of people. They spend a lot of time hanging out in the chaplaincy, which is great if you fancy procrastinating on campus. They also have awesome socials. Denomination-wise, they're mainly Anglicans, to be honest. They're pretty liberal, too. (Oh, and as a side note, it's free to join the society, and you don't have to join the Federation, either - completely free membership!) CU, on the other hand, is a lot more evangelical and probably, therefore, a lot more what people would term 'happy clappy'. They're also a lot more 'hardcore', for want of a better word. They run a lot of stuff on campus. They give out free hot chocolates, teas and biscuits after Top Banana on a Monday night, for example, as a way to demonstrate Christian love and also to share the Gospel, I guess. They also run more seminars and talks, and stuff. But they're also a lot bigger than Focus, so it's a bit more difficult to get to know people, although they are a very friendly bunch and there are of course people who go to both. With regards to the anti-Roman Catholic thing - they're basically a bunch of Evangelicals so, whether you agree with it or not, they're highly likely to disagree with RC doctrines - it just comes with the territory.
While we're on the topic, the chaplaincy runs Sunday morning services - there's an Anglican service at 10:30am (ish) and then a Catholic one at 12:30. However, I didn't find the Anglican one great, so I (being the happy clappy I am... even though I actually have more Focus friends - bizarre!) go to the local Elim in Coventry. I guess I'm lucky in that I can drive, but the local churches are always offering buses to and from camous, and you can also use general public transport.