I posted this on the other thread mentioning CGT on UK property >> Tax implications selling our house in UK
Blevins Franks - 2020 tax guide - snip:
What about selling your property?
In France, the gain on the sale of your French main home is always exempt from capital gains tax
provided that the property is your actual home at the time of sale.
However, under the UK/France Double Tax Treaty, if you are French tax resident, gains arising on
UK properties are subject to French capital gains tax at 36.2% including social charges (plus a surtax
of between 2% and 6% where the gain is more than €50,000). This would apply even if the property
was your main home before you moved to France. You could also be liable to UK capital gains tax
and in this case, to avoid double taxation, you would get a tax credit in France for tax paid in the UK.