It shouldn't be too hard to register with it (http://www.bnf.org/bnf/openat/registration.htm) and I've never had a problem with spam from that site.

I can't get anything useful from the Coeliac UK site atm, 'cos of work restrictions, but I'd guess the info they provide is pretty similar. The only thing to watch out for would be when it was written - the BNF is updated every six months, I'd imagine that the info that Coeliac UK supply isn't necessarily that up to date.