As a straight historical account this film fails rather badly. Most of the characters are artificial, created for the Stars and stars involved. Dowding and Park, historically absolutely crucial, never develop properly - a pity. Goering is cartoonised, but at least reflects his total failure to conduct a strategic assault on the UK.
The flying sequences are, mostly, superb. It was a huge achievement to bring together the aircraft used. As an enthusiast I can pick massive holes in those used. None of the 'German' aircraft have correct engines - they were post-war Spanish Air Force stand ins. And that's before we start on the late war mark Spitfires etc. But who cares? The point is the conflict in the air. It is not close enough to 'real' aerial combat - 10 seconds of terror in 60 mins of boredom. But that is the nature of the cinema medium.
The distraction of Suzanne York (BTW she's not trying to get divorced!) in full 40's u/wear was very exciting when I was 16. At 52 I suppose it still gives me the odd moment!
And look for the hanger being 'bombed' behind Suzanne York and Kenneth More, it really WAS blown up at Duxford - boy, were they cross!
The revisionist historians like to claim that the (actual) Battle of Britain was not that important. That the Germans couldn't have crossed the Channel anyway because of the Royal Navy (probably, but not necessarily so. With air supremacy JU87s would have massacred RN vessels). That the Germans already had eyes on Russia and really wanted to ignore GB as a sideline, possible and a fatal mistake. That the Germans lost the battle, rather than the RAF won it (no statistical basis for this, the Luftwaffe smashed itself against the RAF).
But the Battle WAS fought, and won by the RAF.
Which is why I believe this film is worth a viewing.
Especially the Walton scored sequence, where the Luftwaffe's bombers are hacked down by the Hurricanes and Spitfires of the RAF. An impressively moving sequence of the horror of war in the air. To which the music adds enormously.
I place this film well ahead of the 1990's Memphis Belle travesty in depicting the reality of war. It is certainly on a par with 12 O'Clock High.