Anvil are based in Sussex and have been my vets for about 10 years. It's a small practice and very friendly, very professional. Everything you'd want them to be, they've never sent a vet I wasn't confident in. http://www.anvil-vets.co.uk/
Depending on where you are in East Sussex.... From Forest Row - Duncan Harrison ( or any of his collegues really ) from Priors Farm practise. I cannot rate them highly enough... He is very sensible and matter of fact. Has warned me for and against horses before now and I would trust them implicitly.
If more brighton and Hove way can defo recommend Arundel Equine practise. Used them when we were living over that way, but didn't ever have them for vettings!