Old cycling club mate of my parents Bill, was left behind in France after the BEF withdrew. Managing to evade capture and was taken in by a French family, they used the cover story that he was a cousin from another part of France.
Over a period of time he was taught to speak fluent French, and the resistance arranged false papers for him to make his way down to Spain.
Having made is way across occupied France he reached Vichy France, reaching a town not far from the border, where failing to find the safe house he asked a police man for directions. Even with his flawless French the office then said “Your from Birmingham”.
Tuned out he has spent some time before the war in the midlands so recognised the accent. Copper turned him in and he spent the rest of the war in a POW camp.
When he died (and that was a story in its self) there was a deputation from the French resistance organisation at his funeral