Unless things have changed recently, the initial medical must be done in a JAA country. I am assuming you are going through the UK, so you would have to book yourself a medical at the Gatwick Aeromedical Center. Go to the CAA website for contact details. It is approximately 300 GB Pounds. The renewals can be done anywhere. I use Dr. Knipping in Toronto. I'll have to look up the contact details, but he is on the TC AME list.
Regards
Muddy