You can get your class two at any AME (Authorised Medical Examiner). That's not your ordinary GP unfortunately. Cost is about £150 for the initial, then £80-150 for each renewal depending on the doctor and what has to be done for renewal.
The class one is done initially at Aviation House, Gatwick and costs £400. Renewals can be done with some AMEs and cost £90-200, once again depending on the doctor and what needs to be done.
There's a database of AME's on the CAA website
http://www.srg.caa.co.uk in the medical section.
cheers!
foggy.