GP salaries are highly variable because each practice sets the wages for their GPs independently. GP surgeries are in places with different costs of living, have different levels of desirability, staffing requirements etc, so it is hard to generalise for a whole country. Anecdotally though, a brand new GP in Birmingham will make 60-80k, and that will only increase with time. It's not a way to make megabucks, but GPs certainly aren't poor
Asking about private practice is pretty much impossible though. For a start, most doctors don't really publicise those figures for obvious reasons. Secondly, like any business it really depends on your area, reputation, and experience. I know of some eminent surgeons who are so in demand that they rack up their prices to stupid levels just to decrease their workload, and people still pay. You've got to remember though that this is only achievable after working for 30+ yeard and if you are VERY good
I wouldn't think too much about the salary though. Doctors can, by and large, afford a comfortable middle class lifestyle. Those who don't - either rich or poor, are generally the exception. If you want to be rich, do business in the city