The biggest cache listing site is geocaching.com. (I can't comment on others, e.g. navicache, because I haven't used them.) If you're in the UK and you submit a cache to geocaching.com, your cache should meet their guidelines. Usually it'll be considered by an approver in the UK, who will put a local (UK) interpretation on the guidelines. For example, the guidelines say no caches near bridges, but that's a US terrorist threat thing (a cache container could be mistaken for a bomb), and in the UK it isn't seen as a problem.
The GAGB guidelines, as I understand it, are primarily intended as a starting point for negotiations with big landowners in Britain, for example the Forestry Commission, with a view to getting 'blanket permission' to hide caches on their land. Also, it's hoped that the GAGB guidelines will help to establish a code of good caching practice in this country.
That's how it seems to me, but I'm just a member of GAGB, so that's my own view not an official comment.
There doesn't seem to be a link to GAGB's home page from these forums, but you'll find it here. That should give you a better idea of what GAGB is all about.
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)