You may be interested in joining the British Go Association. This gets you discount at tournaments, and helps support go in the UK in general (they help to find people nearby eah other who play). It also allows you to use the BGA bookseller, who has a large range of books.
Go Discussions is a popular online forum centred around go.
Sensei's Library is an English wiki site with a very large amount of information about the game, including a joseki dictionary.
This website has a large number of go problems you can use to quickly improve your game.
Gobase has a large library of professional player profiles and games, as well as a few large problem sections. Some of the content requires you to register, for a one-off 20 Euro donation.
Go4Go has a large library of professional games, and reviews from Alexander Dinerchtein, as subscription services for a small fee.