Factual error: The RAF policeman at the end is wearing battledress with exposed buttons done up to the neck. RAF battledress had a fly front with concealed buttons and, unlike the Army, all ranks of the RAF wore it open-necked with a collar and tie.
Factual error: The military policemen wear plain black armbands. Their armbands actually had 'MP' in red letters.
Factual error: The Royal Navy officers wear a completely inaccurate cap badge that appears to be a wreath with nothing in it. It actually surrounds an anchor and crown.
Factual error: King George VI was a qualified military pilot and always wore his pilot's brevet above the rank rings on his left sleeve when in naval uniform. This is shown in numerous photographs. He does not wear it in the film.
Factual error: Although her correct rank of Second Subaltern is used sometimes, Princess Elizabeth is also referred to both by herself and other military personnel as Junior Subaltern, Second Lieutenant and Lieutenant. Military personnel know ranks.
Factual error: Numerous military personnel salute while bare-headed in the film. British military personnel only ever salute while wearing headdress.
Factual error: The Grenadier Guards officers wear ordinary rank pips on their epaulettes. Since 1919, Grenadier Guards officers have worn Garter Stars instead.
Factual error: Jack's RAF uniform is wrong on a number of levels. He is not wearing the eagles at the top of each sleeve worn by all RAF airmen. He is not wearing the correct Air Gunner brevet (with a single wing), but in fact wears a made-up badge that is claimed to indicate he has shot down five enemy aircraft. He does not have a cap badge on his forage cap.
Factual error: Jack could not be demoted from sergeant to corporal by his CO. Substantive NCOs can only be demoted by court martial. As aircrew, his rank of sergeant would be a substantive rank, not an acting one (since it was the minimum rank for aircrew). And rank chevrons were made in one piece (two for a corporal, three for a sergeant), so if he was demoted he would have a new set of chevrons, not the top chevron removed as depicted (not only would this be impossible, but it would be a clear indicator that he'd done wrong and given he is still an NCO this would be demeaning).
Factual error: Jack is addressed by everyone as 'Airman', not as the correct 'Corporal'. The rank of Airman does not even exist in the RAF.
Factual error: Pretty much every medal ribbon shown appears to be completely made-up.
Factual error: When Elizabeth gets on a double-decker bus and meets Jack for the first time, she is asked to pay for a ticket which is issued from a machine. These devices were not available until the 1950s.