Before EASA demands changed things it was always possible to fly privately a UK registered aircraft within the UK airspace on an ICAO licence. The UK was one of the few countries to allow this. Many ICAO countries required some kind of formality. Meantime LastStandards has explained the current position. You have 2 years from 1st January during which you do nothing unless you choose. The whole point of JAR and then into EASA (with a wider agenda) was to validate your licence for use anywhere within euroland. I can't believe that the UK will ever seek to prevent you flying a UK registered aircraft anywhere in the euro world using a French EASA licence.
It is currently a waiting game.unfortunately. Time will tell.