Further to my earlier post, the case I was referring to was for a hip replacement (hip operations are so uncool) the recipient was an elderly lady in east anglia somewhere (I saw it on Anglia news) she went to France and the cost (including airfares,etc.) was less than if she'd had the same operation privately in this country.I think (some doubt here) she sued the NHS and the judge ruled that if she had waited a reasonable length of time i.e. 4 months without having the op. she was entitled to go privately and send the bill to the NHS.Unfortunately although she won her case there was (in her particular instance)some reason why they didn't have to reimburse her but I don't know what that reason was, but the precedent was set.
You could start a UK thread on this subject, I'm pretty sure there are some lawyers here.
If I can find out any more, I'll post.