I will make an argument for GPs. Yes, consultant neurosurgeons likely have a higher average income, but becoming said consultant neurosurgeon takes many years. Long training, PHDs, academic fellowships etc. Becoming a GP takes 3 years post-graduation. A GP who became a full-time partner early on could have a half million pound 'lead' or more in terms of cumulative earnings vs a neurosurgeon by the time they reach consultancy. The neurosurgeon will then start catching up, but again: that income is likely to be skewed toward the latter end of a career as private income is heavily experience-dependent. By retirement, the neurosurgeon will most likely have earned more, BUT for the majority of the working lifetime he would have been behind the GP. Is it the final wealth on retirement that is important, or is it how wealthy you were through your lifetime?
Very difficult to quantify, but just an angle to consider.