Was doing my multi engine course (on the Varsity) at Oakington whilst this was being filmed at Duxford, and a number of our instructors who had quite extensive Spitfire experience in their younger days were 'seconded' to the film.
We were actually night flying at the time but the nice high pressure system gave good day weather but foggy nights, so we would all go down to watch the action. The scene with the 109's and the French Chateau - a nice bit of 3ply on Southern side of Duxford was particularly impressive for all the watchers on the other side of the trees!
It was also quite a good time to be stooging around East Anglia 'cos you never quite knew what would appear on the wingtip! My final memory was the morning after our graduation a full beat up of the Oakington Mess by (I think) a 9 ship of Spitfires at what seemed like first light and roof height.
Happy Days