Hill House, an S.O.E. training facility, years supposedly 1943/4, record played in the lounge..Charles Trenet--La Mer. Recorded in 1946 therefore could not have been played in '43/44.
The British didn't say "classified" during WW2: they said "secret" or "top secret".
Although set in 1941, there's quick shot of Queen Elizabeth II, seated, in pale pink gown. At that time, Princess Elizabeth was 15 and her photo would not be on the walls.
This is 1941. In the background the radio plays Le Mer, sung by Charles Trenet (at the training camp.
Trenet only composed this song in 1943 and the first recording of any kind was in 1946.
At the conclusion, we discover that the young man supposedly killed in the explosion had in fact died in a work accident. His funeral had in due course taken place, and his body had later been stolen from the grave and taken away by the secret agents to be used in this way to fake the suicide of someone else who had actually been killed on a spy mission.
The whole plot hinges on this.
Yes, his head was blown off, but forensics in the 1940s was sufficiently advanced that they would have known they were not dealing with a body that had been dead for several days, and had not been killed in the explosion. One obvious clue would be the total lack of blood at the scene.
The French agent at the beginning of this episode pronounced basic French like 'putain' incorrectly.