A word of advice that was given to me on this board, and I'll pass it to you;
Bring as much of your medical history here as you can. This way you can prove you have been on the medication for x amount of time, have had no issues, etc. Most GOOD doctors will do their own tests etc, then prescribe, then have you come in for a refill of the script and a check up to see how you're doing on the meds.
I also think it depends on the GP as said above. Some GP's feel comfortable perscribing these drugs, some would feel more comfortable sending you on to another doctor or psychiatrist.
I think a vague plan of action would be get as much of your medical history as possible, maybe even a note from your doctor expaining the situation, come over, find a local GP
http://www.nhs.uk/servicedirectories/Pages/ServiceSearch.aspx?ServiceType=GP and go in and speak with them. If you get no help there, go to another. This is what I had to do to get my medications here. I had to find a doctor who actually listened and cared about their patient, the medical records I had sent helped a lot too!
I've only had positive experiences with the NHS and had a bad GP to begin with (would end up crying every time I walked out of their office!) but have had no issues with scripts, check ups, apts, and any care I need

Good luck!