Thank you for your advice and experience. I just realised my passport only has a couple of pages left, so I need to renew. I will definitely go, but not anytime soon.
I think you are right, all I'm saying is that if I fall ill in Thailand, having paid NI until I was 65 and paying UK tax on my income it could be an option. As it stands I have to return for treatment, whereas our NHS would save money if I am treated here.