This is the kind of thing you can have fun with. Why "invade" the UK? It's not like the French don't have plenty of their own beaches on which to practise invasions.
I can just imagine the nationalist zeal such maneuvres might unleash. I have an image of people standing on surrounding hills with pitchforks and yelling 'go home Froggy bastards! Britons never will be slaves!' and then going home to watch Countryfile.
(P.S. and I can imagine the French sailors on the ships 'Yeah rosbifs! Shake your little pitchforks, 1066 eh!' or some such and then everybody locks and loads and they all go off together and shoot some religious nuts in Mali).