The French health system is one of the best in the world. Massive pay-roll deductions both from workers and, especially, employers has resulted in a system which is well-funded and full of resources. The care tends to be excellent and waiting lists for treatment are virtually unknown.
However, the system in contribution based. For all but real emergencies, you have to show your Carte Vitale. This card contains a chip showing that you have paid contributions and are entitled to received treatment.
If you are a British resident visiting France for a short period of time, you need a European Health Insurance Card. You can get one here :
If you are newly resident in France and have found a job, once you have worked 60 hours a month for more than 3 months, you qualify for free medical treatment. You don’t have to wait until you receive your Carte Vitale (which can take a while to arrive.) In the short term, the doctor will give you a paper that you have to sign and return to the CPAM.
All this is organised by the CPAM – and you should register with them as soon as you become resident in France.
People receiving a British pension are entitled to free medical treatment if they move to France. All you have to do is to get an E121 from the NHS in the UK and present that to your local CPAM in France.