Though not a quack, I'm surrounded by them in the family and as friends. None of them advise BUPA or any other private medical plan. The cost of seeing a consultant privately is not much (sub £100, often), and if there's anything that needs treatment they then push you into their NHS list and in most cases the wait is not long.
Put the monthly subs into a savings plan, and go to King Eddy 7's Hospital for Officers (if appropriate) for surgery, which gives discount for former officers and spouses. Queen Mum used it extensively. My old Mum had her hip done there for a lot less than the local BUPA place.