I am quite sad to hear that a person of your mathematical calibre is not in a profession which uses this skill or is not in a profession that rewards you for your intellect.
I know money is not everything and the richest guy in the world is not the cleverest and conversely the richest is not the cleverest but it
ought to have some correlation.
Regardless (and I am sticking my neck out now), I would say you are not an ex-public schoolboy / don't have the contacts for finance. From my own experience, I have seen and worked with many mediocre candidates in top jobs (though never technical), being paid somewhere in the region of £0.25M a year, holding managerial positions. Admittedly to do one of those jobs, one need to have (not nice) people skills,
Whilst I don't want to put you off the medical profession, I also have friends, who at 18 wanted to save lives (and the world for that matter) only to be disillusioned after 5 years medical training and 70+ hour weeks working as a junior doctor.
Add to that, being a surgeon (as opposed to physician) has a lot to do with fitting in and unfortunately, politics plays a major part.
If you had sought advice before turning your back on finance, I would have suggested you try (finance) abroad. You may find the working conditions, including prospects, colleagues, work / life balance, would have suited you more.
Nevertheless, I wish you success in your chosen profession.