When the U.S. soldiers are mocking a Home Guard unit drilling nearby, they say things like "they haven't even got uniforms." This would appear to be the case as you can see them wearing only LDV (Local Defense Volunteers) armbands on top of their "civvies." This was the case when the force was first formed early in the war (1940) well before the U.S. entered the war after the Japanese attack on Pearl Harbor on December 7th 1941. But by the time the GIs arrived in Britain in 1942, all units of the Home Guard were fully equipped with uniforms, weapons etc.
At about 53 minutes and 14 seconds into the film, a map of Europe is seen hanging on the wall. Judging by the color-coded countries seen on the map, it's obvious a post-WWII European map. Germany, for instance, is clearly separated into two sections --- namely West and East Germany.
At about one hour, one minute and 17 seconds into the film, a panoramic view of Tangiers is shown but it's the present-day modern city of Tangiers, complete with high-rise modern hotels and harbor rather than the 1940s wartime Tangiers.
Although the film takes place from 1942-1944, Dana Wynter's hair style, the cut of her clothes and uniforms (no shoulder pads) and skirt lengths (too long) are strictly 1956.