A newly-hired doctor straight out of med school makes around £23,000 for a 56 hour week but it increases rapidly in the years after that to around the £50,000 pa mark by the time they are 5 years out of Uni.
New GPs do get upwards of £55,000 but it takes ten years to train as a GP: 5 unpaid years in med school (which will more likely than not cost £15,000 in fees from next year, not forgetting the cost of living for 5 years), 3 years in a hospital then minimum 2 years as a trainee GP before you have to buy your way into a practice. Hence why WWW's mate who is just becoming a GP is 28.
Dentists do a lot better than doctors for cash, they're usually earning well over £50k by the time they are 25. Outside the City there are few better jobs for high earning potential at an early age...