Hiya,
You are lucky as there are several clubs in Sussex Most clubs do a taster session or trail period but ask at whatever club you choose joining. the club membership allows you to shoot in more competitions.
Best advice is to make contact and get along to one of the clubs to have a look round and make sure its for you. You will get good first person advice and most probably a chance to shoot and look through lots of different kit.
https://sites.google.com/site/sihftsite/
Should find some contact details on here for local clubs to you.
Advice on rifles is very personal. If I was you, I would shoot a bit with your Ultra until you have decided what is for you and how much you want to spend. There are sections for .22 shooters in most comps but not loads of shooters as your right, the loopier trajectory does make it more difficult.
If your thinking of staying with PCP then your probably talking at least £450-500 for a set-up including air bottle and scope. But if you've already got filling equipment and a scope that will do then an AA S400 between £250-£350 second hand will keep up with most stuff. Scope is dependent on many factors including your eyesight.
Word of warning!!! You can and will probably want to spend serious wedge on this hobby, but its not really needed, there are just lots of nice things that you never realised that you NEEDED
Si