Well, as many have stated this is unlikely to raise any major reaction in such a secular country as UK is (or Czech Republic, for that matter, should I relate to my own country). People just don't care enough to react in a measurable way. Sure, there might be an angry phonecall from some random nutter but hey, you might get an angry phonecall from some random nutter for posting a yoghurt ad promoting calcium.
I vaguely feel that there's a subtle difference between advertising God and advertising no God. If I were to put my finger on it I'd probably reason along the lines of that one is offering people something, whereas the other is taking something from them, but it's mostly just a feeling, really.
Either way, if the ad says PROBABLY, there's absolutely NOTHING ANYONE could have against it. I don't find it funny, I don't find if offensive, it's just an unusual ad, that's about it.