Things seem to be getting a little tangled here -
ANY JAA medical is now valid for a JAA licence - irrespective of which JAA country issued the medical and which country issues the pilots licence.
If you elect to do this through the UK CAA - then (I believe) the only place to get a UK CAA INITIAL class one is through CAA Gatwick - renewals can be done anywhere. I do my renewals, here, in Florida.
If Stud3 wants to go 'professional' then it's a darned good idea to get the class one first - also a really good idea to go through each of the tests with local medics/opticians etc. first if there is any doubt about passing it with the UK CAA.
UK CAA can also issue you with an FAA class three if you ask them at the time!!! Save you doing another medical in USA.
DONT FORGET TO ASK FOR STUDENT PILOT CERTIFICATE WHEN DOING INITIAL FAA MEDICAL!!!!