Interesting questions Across... most of which have been answered but on the private versus NHS...
Does the NHS pay for part of private care then private insurance picks up the rest? If not, does private insurance pay 100%? How expensive is 'good' private insurance? And I assume having private insurance doesn't allow you to 'opt out' of paying NHS contributions?
Private insurance is a luxury that basically allows you to queue jump AFAIC. Depending on the level you have, you can rest easy that there is no waiting. However, you have to be referred by the NHS and that can be clunky to deal with. We had private insurance for a number of years (via DHs job, then when he retired we paid for it ourselves before it got horrendously expensive because of our ages so we had no choice but to give it up).
No you can't opt out of NHS contributions.
It did mean my DH, who had a heart condition, could have a procedure within a week instead of a worried wait.
I've had eye surgery and paid for it myself and I'm due a dental implant shortly which might involve bone grafts, that will cost me a minimum of £3,000 probably more, as Asking said... dental and eyes cost a lot. I feel sorry for elderly patients needing cataract operations, they have to wait in a queue to have it done on the NHS.
However, I cannot praise the NHS highly enough in an emergency. I've recently experienced this with my DH and encephelitis, he could not have been looked after better with 4 GP appointments in a 5 day period followed by a 2 weeks stay in hospital, all for free.
So there is good and bad basically. The NHS is horrendously overstretched but at the sharp end they are wonderful.