Just while you're doing that, your old GP should still be able to prescribe medication for you- they can fax it to any pharmacy you choose.
Good luck. We've been with the same GP for a long time but they tried to offload us when we moved a few streets away but we fought back and won as there were no vacancies at any other local surgery at that time and we were offered somewhere in Peckham by the PCT. I was also at that time having ongoing medical investigations for something and did not feel it was a good time to be forced to change GPs.