Loved this -- probably one of the funniest Will Hay films I've seen. I far prefer the pictures he made with Charles Hawtrey to the 'classic' teaming with Moore/Marriott, and an excellent supporting cast here includes Peter Ustinov and Frank Pettingell (of "Gaslight" fame).
I always find Hay funnier when he is being a pompous but resourceful twit rather than simply an arrogant incompetent, and here his schoolmaster character is put up against the Nazis and manages (with assistance) to rise to the occasion... aided by the fact that his opponents half the time are even bigger buffoons than he is. A sharp script relies heavily on verbal humour, with two outstanding scenes that riff on the absurdities of the English language. The invasion plan sequence in which Hay improvises strategy wildly in a cascade of puns while attempting to pick a German general's pocket deserves to be a classic of the genre (take them from the flanks in Lancs to keep the Paras all tied up in Notts... but don't get caught with your Panzers down in the Severn Tunnel).
There is also a clever yet natural-seeming series of gags making use of an asbestos suit, some of which you can see (and enjoy) coming in advance, some of which I didn't! The final reels of the film didn't work quite so well for me, chiefly because I couldn't help but be aware that with all those antics the plane wouldn't have lasted for a minute and had some trouble suspending my disbelief in the name of comedy -- it's always funnier when it's actually physically plausible, however far-fetched. (The ingenious tactic by which Hay contrives to prevent his friend Professor Hoffmann from drinking a glass of poison by triggering his "Heil Hitler" reflex precisely at the requisite moment, for example.) Up to that point I would have rated the film at a definite 8/10; I still rate it a solid seven.
The contrast between English and American propaganda films was never more marked; see also "Night Train to Munich", "Pimpernel Smith" and even "The Lady Vanishes" for Englishmen working against the Nazis who simply don't take themselves all that seriously.
