I am a duel National UK French citizen that emigrated 11 years ago with an S1 The S1 covers the basic health care costs and provides the French with a way of recharging the UK for that part of your health care. Your Carte Vital has a special number that allows this. Over and above this you really need health care insurance ( mutuelle) ours is €300 per month for two of us covers a certain amount of dentistry, glasses, consultant visits scans private room in hospital, ambulance etc. If you don't have a mutuelle you won't die in a corridor or on the steps of a hospital but it makes things easier. If you don't have an S1 then there is a very basic state funded access to the health service. The S1 from memory is only available to retirees and is or was complicated to get. Wading through French bureaucracy to get your Carte Vital is not for the faint hearted either and you need to be competent in the language, there are no translators. Most people have a mutuelle usually through their work or union with some form of subsidy.