Thank you Karen. Much useful info here. Yes, I had an S1. I have just had a communication via the Impots website to say that I will be refunded part of the social security tax payment: the CGS-CRDS component (9.7% of income). This leaves the PREL-SOL component non-refunded. I Googled PREL-SOL and this brought up a useful website bh-assurances.fr/tax-information where it is explained as follows:
The French government has changed the law regarding social charges. Before last year, the global rate for social charges in total was 17.2%. It was then composed of 5 different types of tax). One of them is called Solidarity levy and it was at a rate of 2%. This social charge is to help for French pensions so nothing to do with French health system.
Therefore, even if you are under an S1 and therefore should not pay social charges, you will have to pay the āprelevement de SolidaritĆ©- Prel Sol. However, now the rate is 7.5% instead of the 2% is last year!! Good measure for French people as this tax is only applied to capital gain/interest/rental income and not on income from pension or salary but bad news for people who are not affiliated to the French health system or are under the S1 system (meaning the UK reimbursed CPAM for your health expenses in France). Now the rate is CSG at 9.2%, CRDS at 0.5% and Prel Sol at 7.5%.
So, as my tax is on rental income, I suppose there is no way of avoiding the 7.5% for PRE-SOL. Any suggestions on how one can avoid this welcome!