The best thing about the NHS compared to medical insurance is that the cost to the consumer does not depend on risk. What are the chances of getting private medical insurance to cover you for a heart attack, at an affordable price, if you have had a heart attack before?
I had private healthcare paid for by my employer for many years without ever using it. At 64 it cost them about £600 a year, at 65 it jumped to £1,800 as I was deemed a bigger risk being older. So just when you need insurance you can't afford it.