Hiya, there's a few good ones. Jo Barry is a dressage trainer, her yard is near the newbridge roundabout and she's excellent. There is also Fiona Flynn, Anne Comrie or Jane Fegan who are all sisters. Fiona and Anne mostly teach at Houston Farm riding school in Uphall(there parents own it) and Jane has her own yard. Have a look on BHS website for them or www.hfrs.co.uk
When I lived in Edinburgh last year I had a few lessons with Anne at Houston Farm and found her really good. She was so good in that she use to give me a private lesson at 8am every Tuesday morning! Would definitely recommend Anne and Houston Farm, which is not far from Edinburgh.