Bumping this (reasonably) old thread to once again recommend the services of Peachy Health (
http://www.peachyhealth.co.uk/services.html) for MSA medicals. I've recommended two people to them over the last year - one had a small difficulty with his local doctor, and the other one was being overcharged.
I accompanied the last one on the day, and have to say they're lovely people, and Marios (not entirely sure how to spell that) was very professional. The medical was done in about 20 minutes, for £35, and at the weekend with short notice. They also know the ins-and-outs of the MSA medical form - which some doctors struggle with.
Would recommend them very highly for anyone looking to have a medical for their MSA licence this year.