I was on a course at Rolls Royce Small Engine Division at Leavesden in '69 when the airfield was "strafed" by a bunch of 109s which were then attacked and hotly pusued by three Spitfires. Unlike today's airshow dogfights, this scrap looked very realistic. It doesn't appear in the movie, and Leavesden in '69 looked nothing like it did in 1940 so I guess it was a practice run for a proposed scene.