You will need a UK sticker, doesn't necessarily have to be on the number plate, it was Boris's idea to emphasise the countries unity after Brexit ???
https://www.brittany-ferries.co.uk/...ion/do-i-need-a-uk-sticker-on-my-vehicleTo comply with the law we put a UK sticker on but I see many people still using the GB sign either out of ignorance or defiance. Not worth rubbing the Gendarmes up the wrong way for the sake of a sticker.
The Gendarmes really couldn't give a damn!
Until Macron or their union tells them to be difficult. Had it before now with boats when some british / French political argument has caused the gendarmes or douaine to be wound up to full bureaucratic Frenchness. Got inspected by all three inc local plod going through every bit of paper and doing so at several ports the last time round and that time it was about union fears of redundancies so they felt the need to prove their worth.. Best response is to put both plates on.
Have also heard of Britsh cars being targetted though never experienced that myself