The London bus used is a Routemaster which were not introduced into service until the late 1950s.
Much of what is depicted during the parachute training phase is incorrect.
Whilst the Poles may have formed a parachute training school in Scotland, the actual jumps were all completed at RAF Ringway which is now Manchester Airport.
The instructor is shown as British Army with those on the ground having Parachute Regiment insignia. In Britain the parachute training is done by the Royal Air Force and has been since WW2.
The instructor in the plane also wears his parachute wings on both arms instead of the right arm only.
Even by 1944 the aircraft used for parachute training were old bombers where the students exited through a hole in the floor and not through a door.
Early in the film, at a German staff meeting, one of the officers refers to 'Sir Winston Churchill'. Churchill wasn't knighted (becoming 'Sir') until 1953.