At about 1:39:25, where soldiers and civilians are in line, a character directs them (twice) "soldiers to the right, civilians to the left." Then he says "civilians to the right:" and then again (once) "soldiers to the right, civilians to the left." That would have caused chaos.
When General De Gaulle flies to his first visit with Churchill in London he uses a Beechcraft 18. When the Airplane takes off on its right upper wing the US registration N2913B is clearly visible.
This Beechcraft Model 18 was built as a model D18S in 1953 and was registered under N2913B for the first time at 19th May, 1953.
DeGaulle enters an unoccupied flat in London, empty for weeks. You can hear the sound of the tall clock, still ticking, but nobody wound it every day.
When going to London for the first time, De Gaulle goes by some planes, one of them is Douglass C47 with D-Day insignia. Both is impossible in May 1940.