I'm curious, if you go to the doctor or a hospital, do you not currently have to show proof that you are eligible for care under the NHS? Here in Ontario (Canada) we have to present a Health Card to show we're covered by OHIP (our version of NHS). It looks just like a driver's license but is a different colour, has a photo of you and expires every 5 years I think. The old "red and white" healthcards as they were called (because they were red and white, whereas the new ones are green) never expired and didn't have a photo. Apparently several years ago the government discovered that people were commiting fraud with these cards, and switched to ones with photos that you have to renew every 5ish years (apparently people who were not eligible for OHIP were using cards that did not belong to them to get free medical care.) It's kind of a pain in the ass to have to renew it every few years, but it's better than letting some "johnny foreigner" use my tax dollars to cheat the system.