I use Micromark stuff. Their starter kit got me up and rinning with some of my custom bitz ive made.
Takes some getting used to, but you'll have that with any casting set.
http://www.micromark.com/COMPLETE-RESIN-CASTING-STARTER-SET,8174.html EDIT:: ohhhh didnt see ya were in the
UK... hmm... well Im afraid I cant recommend much in that case, sorry bout that :/