Let's say it starts around £60k, but there are so many things that make it vary (usually upward):
Patient count, Area you practise medicine in, whether you're a private physician or not, how many partners are in your practice, whether you're a partner or just a locum whether you have a sub speciality (diploma's) and take on other GP's patients, research, practise target's met, Locum'ing etc.
I'd say up here it's about £75k+, but sometimes it can be as high as £280k. I know one guy who doesn't work weekends and earns £150K!! Lucky bugger!!!