You have got your history mixed up.
The British never occupied Normandy unless you consider the Allied Invasion with the US army or you consider the English as British. Fact is Britain was conquered by the Romans, the Vikings and later the Normano-French.
On the other hand the Franco Norman Dukes and French counts occupied England for a long time. For more than 300 years French was the Royal language of the English court. You can even look up how the Englishry law demarcated the noble Franco Norman class and the common English peasantry. The French have left an indelible mark on the British isles be it in the castles they built or the effect on the English language. 29% - 40 % of English words come from the French. Today most English names and surnames come from French. Heck even Winston Churchill`s surname Churchill came from the French word Courcelle. All of this was due to the Norman conquest of England by William the Conqueror which is described in the Bayeux Tapestry where the Normans are called as Francii and the English as Anglii.
en.wikipedia.org
Also do you notice how the word "Frankly" in English language even today means being truthful and sincere.
The colonial French did perform poorly against England but that is a different story.
Anyway here is a picture of the British passport which still bears the
French phrase "Dieu Et Mon Droit"
en.wikipedia.org
en.wikipedia.org
en.wikipedia.org
en.wikipedia.org