Theism is an intensely personal thing. You can’t teach belief nor can you accurately measure it. People, especially us reserved Brits, usually keep such things private – unless bitten by the baffling evangelism bug. We’ll never know how many people believe in God. Sure, the census reveals which religion people associate themselves with, but many of them could actually be atheists. When it comes to assessing the number with real faith in the man upstairs, we don’t have a clue.