Here are links to some organisations and Clubs.
The Federation of Northern Aquarists Societies. Looking after the welfare of the Northern aquatic clubs in England, including Open shows and breeders schemes
The Federation of Scottish Aquarist Societies. The Federation of Scottish Aquarist Societies consists of 13 Aquarist Societies throughout Scotland who hold regular meetings and yearly Open Shows.
The Federation of British Aquarist Socities. A well known aquatic federation mainly based in the South of England.
Sheaf Valley Aquarist Society. A south Yorkshire-Nottingham club re-born, that has its own web site and forum