I've not (yet!) had training sessions from any of these people so I'm really not qualified to answer your question!, but I will be moving to Wilts way next year and have been researching potential trainers to have lessons with and I've found the following people and they have websites you might find useful:
Hopefully you may get some replies on here of people who have trained with them or can recommend some others too!
If you want to be sure to be steered in absolutely the right direction (which, I'm sorry to say, not all dressage trainers will do), Annabel Scrimgeour is in Wiltshire. She judges at big CCIs and trains some top names. I've never been taught by her though so can't say what she's like.
If you're more Glos way, Tor Brewer knows her stuff.
I hear very good things of Amanda Brewer too (no relation afaik).
Andrew Bennie is good i have him... he is also a listed dressage judge (grade 2 ) which is helpful and also a international candidate judge for eventing
just to let you know jonny that K27's suggestion of kingfisher would be too far for you Thats where the Phoebe clinic is being held-so 1hr19mins i think we worked out??