Found this pretty sweet website calling itself 'the UK organic search engine.'
However they also list companies producing wheat free, gluten free, dairy free, sugar free, lactose free, kosher and halal.
The site has listings of companies offering gluten free -
places to eat
There's even a couple of links to websites selling allergy cards in several languages.
I could have done with one of those when I was in Italy! Repeatedly saying 'me no flour!' at Italian waiters doesn't exactly work!