GP and A&E treatment are free to all. (Good luck with getting a GP appointment). In-patient treatment in an NHS hospital will be charged at cost + 50% to non-residents. In practice, this might depend on how long you've been away. I moved to Thailand in 2009, but in 2016 I was taken ill over a weekend, GP surgery closed so I went to A&E. When I gave my name and date of birth the receptionist said, "Oh, that's 36 XXX Road, then?" obviously I replied yes - so I was still on the system 6 or 7 years after leaving. Within the last year I tried searching for my record on the NHS app, nothing doing. I can't remember my NHS number. Clearly I have now become a non-person as far as the NHS is concerned. I get insurance before I go to England now.