You will need to go through your vet as physio's won't treat your horse unless with the vets agreement - which also means that your vet should be able to give you some names. However, if you are looking for recommendations then I use Jose (can't spell his last name!) to treat mine every 6 months with the vets agreement. He is hands on and has put me to shame on a couple of occasions particularly as I pride myself on looking at my horse carefully. My 2 best misses to date have been 1. not checking under my saddle to check the flocking is even 2. looking head on at my horse - if I had I would have seen that his eyes weren't level until Jose manipulated around my horses head and it went straight again...
Jose is a registered Spanish vet (not practising over here) which gives me a little more peace of mind when he treats my horse.
Jose is a chiropractor. If you want a good physio recommended by Liphook then Jenny Stephenson is the person for you! If you want a masseur only then Beth Butler is who I use. If you would like the three numbers (I also use Jose) then PM me!
I would agree that if you use Jose or Jenny then your vet will need to know.