When Nutmeg and Beeswax squadrons are getting airborne, the lookout reports: "12 Spitfires taking off." The aircraft used are Hurricanes, and are referred to as such throughout the film - including by Baird, speaking in the control room immediately after the lookout's report.
While almost all the aircraft in the movie are Hurricanes, the fighters shown taking off right after the lookout's report are indeed Spitfires. You can tell by the way their landing gear folds outwards towards the wingtip. A Hurricane's gear is set further out on the wing and folds inwards towards the body of the plane. The video quality of this scene is not up to the high quality found in the rest of the movie, and it's obviously stock footage. Unless it was added to later digital versions of the movie to correct the continuity error, no error actually occurs.
While it may appear contradictory that Moon informs Baird he is to fly as his Yellow 2 and later, when they are both running to their planes, says: "Don't forget, Septic, you're flying as my Black 2," , it is clear from the action that these statements actually refer to different sorties.
There are several shots where it is obvious there is no glass in the front part of the cockpits of the Hurricanes. When Baird slides his canopy shut, his fingers protrude to the outside.
During Septic's transmissions after the dogfight, there is no background sound of engine, as though he were speaking in a silent studio.
Baird takes the German altimeter from the bomber he has just shot down, as a trophy for the messroom wall. However, when he later puts it down on Moon's desk the "altimeter" is a British rev counter (the face is marked "RPM").
At the end of the film, the camera pans out to show a light-coloured runway with taxiways running off it. However, the airfield was simply a grass field without proper runways.
When all miscellaneous aircraft are scrambled prior to the Luftwaffe raid, the Hurricanes involved have fuselage markings of narrow white and yellow bands that were not used until 1942.
Jack Hawkins' Group Captain "Tiger" Small tests the fighter station guard by trying to bully his way past Peter Jones' sentry without showing his ID. Forcefully challenged by the sentry, the Group Captain shows his ID but it's upside down yet still gets the sentry's glanced approval.
In the first scene when Septic walks in to speak to the airmen, they scramble to their planes, crazily running out of the room leaving Septic (who can't fly) all of a sudden standing in the room by himself. Oddly, there is a man under a table to his left, moving his leg - presumably film crew.