If you can find them over in the UK, Gray Tree Frogs are pretty damned good frogs with lots of personality, aren't as big as WTF's (so if you have a small tank like me, you could easily house one, maybe even two), and they are nice and resilient, so they can be a good beginner frog. The only issue I might see is that they are an American species, so they might be tricky to find over there. Good luck to you if you decide to look for one though.