I had a stroke of luck, it was obvious that the NHS wasn't going to anything until the knee actually "failed". Not entirely their fault, the government seems to think they can care for all of us for next to nothing. I know somebody whose knee "failed", he might of embellished what actually happened, but it wasn't nice. It was only as an emergency that it was done, seems that's what happens these day. Sorry, I digress, stroke of luck was that my wife's firm who provide health insurance as part of employees salary package changed their insurers to a company who would accept pre-existing conditions unlike the previous firm, Aviva.
I had already decided to do some research and found this particular prosthetic with a 30 year warranty. I then had to find a surgeon who was able to do the job as it isn't a standard NHS version. I had been told that the NHS knee would only last 10 years hence the research. However I had an interesting conversation with my surgeon who told me that most of his NHS work is "resurfacing" old knee replacements and he said that most of them were 25 years old, so not as bad as I had originally thought, but I'm pleased I looked for some better (I hope).
They currently cost about £12k but the NHS are doing trials with them, in fact my surgeon told me that he was offering the particular knee I was having to NHS patients as part of a trial, too late for me. To be honest I was personally at the point where I would have robbed a post office or bank because both knees were bone on bone. My surgeon's first words to me were "your knees are totally knackered", he spoke my language OK, no technical jargon, say it like it is.
I actual asked my GP last year when I was having a bad couple of months, would the criteria be different if I went private, she said not. My other half has Private Insurance through work which would cover, but the way I understand it the referral goes to them and then you go to one on there list. At the time most days back then I was having to use a walking stick to walk the dog . Though the x-ray she sent me for reported only moderate disease, where 10 years previous I was told on arthroscopy I had severe disease. Though they did other things like removing floating bodies and trimmed stuff at the time, I was generally much better. Thank you!
Hope that helps.