This is what the U.K. F.O. ‘Living in Spain’ advice pages has to say.
“If you are in receipt of a UK old age state pension or long term sickness benefit, obtain an S1 form (previously E121) from the International Pension Centre on +44 191 218 7777. Once issued, register the S1 form with your local INSS office, before you register with your local GP surgery and obtain a medical card.”
This is for people moving from UK but it should apply to you in two ways
1) As a EU citizen state pensioner, you are automatically entitled to the service. 2) The S1 form is to ‘decouple’ a person from one state’s health system to sign up for another – so the person does not get two bites of any NHS cherry.
France may have some other form than the UK S1 but there will be an equivalent, to achieve the same result.
How it all works in practice I have yet to find out. But I can report a most encouraging comment by my UK G.P. who told me that her father (who must be in his mid/late 70s) has been living in Sp for 10 years+ and her view of the health care he has received is that it has been “excellent”.
I’m sure others will chip in with personal experiences