The British RAF did in fact operate the American-built Consolidated B-24 Liberator. They were ordered in 1940 but were only operational with the RAF from 1941. The RAF used the Mark II Liberator primarily in Coastal Command and Bomber Command (as depicted in this film), but also for carrying heavy cargo. Most of the aircraft were based in Britain and operated over Northern and Western Europe, but they also saw service in North Africa and the Middle East.
The RAF only used home-based Liberators as maritime patrol aircraft. They were employed as bombers in the Far East.
One of the aircrew wears an Observer 'half-wing' brevet on his chest. As it was set in 1944, the brevet should have been the Navigator brevet which had replaced the Observer brevet about three years earlier.
In the opening dogfight sequence, set during the Battle of Britain, the Spitfire depicted is a later Mk.IX, which did not enter service until three years after when the dogfight supposedly took place.
Perhaps it was done for a reason. But in the dogfight sequences there is no swastika visible on the tails of the German fighters. The normal Luftwaffe "livery" was the German cross on the wings and fuselage and the swastika on the tail.