I was with BUPA for about 15 + years. My cover, paid by my employer, covered referrals from my NHS GP. It didn't cover anything to do with pregnancy or accident and emergency type stuff or checkups.
In my time I had the following carried out:
Ingrowing toenail removal.
Some kind of puss filled boil on my back removed.
Physiotherapy for a back problem.
Gall bladder removal.
Removal of an enlarged mole on my ankle.
All by referral from my NHS GP.
The main benefit to me of using BUPA was that any work done was, to a degree, at a time and date of my choosing.