I missed
As a LAPL is valid throughout EASA, you can fly your Uk registered homebuilt anywhere within EASA.
Sorry.
With regard to
You will need French DGAC approval though, to operate a UK registered 'Permit to Fly' aircraft in France.
My aircraft is covered by this
Arrêté du 22 mai 2001 relatif au survol du territoire français par des aéronefs de construction amateur immatriculés au Royaume-Uni | Legifrance