My wife had an investigation (not BUPA) and it was no hassle. An op followed and again no worries. She was then called for a post-op check 3 years later. The insurers tried every which way to get out of paying and even refused to pay little sums like £25 for equipment. In the end they paid everything.
We jacked it in this year when her insurance premiums hit £1200 per year. The premiums go up at medical inflation rates which are at least double the national rates.
We asked how much the proceedure would cost - answer £1200 or so.
Now on we are with Beneden Healthcare - tenner a month - and will self-insure for anything not covered.