One minor niggle - those two maps asked different questions, and as such, may not be directly comparable. It may seem like a nitpick, but as I recall, there have been separate surveys in the UK asking about religious identification and about belief in God. In the former, more than 70% identified themselves as Christian. In the latter, around half said they believed in God. So the number identifying with a religion does, it would appear, have a tendency to outstrip the number professing a theistic belief. It's likely that cultural identity has an effect there.
Edit - and they're 14 years apart!