Avoid the book of the same name clumsily written by John Foley if you ever see it, based on the film's screenplay by Jack Davies. The main thing here is that the film was a showcase for the mammoth personality of James Robertson Justice, it would be virtually nothing with someone else in his role of frosty crusty portly professor. The book is nothing without him; get the DVD.
In WW2 acidic high-up professor (JRJ) has to get into Nazi-occupied Europe to try out some scientific experiment but gets captured and sent to a POW camp in Germany to his disgust. Then he has to get out again with the help of his room-mates who eventually discover just how important he is to Winnie in London at least. A lot of old British actors were paraded here, but particularly manic Stanley Baxter (x2), lascivious Leslie Phillips and poncey Jeremy Lloyd, all making for a comfortable familiar ride. JRJ surpassed himself, evincing stoical but disdainful contempt for everyone British or German and his surroundings, barking orders to all lesser mortals and generally displaying an organisational brainpower not usually found this side of Mount Olympus. Favourite bits: Phillips immortal impatient leg-crossed line when JRJ as a Red Cross Inspector is imperturbably wasting time in front of the German guards; and almost everything JRJ uttered during the film.
All in all, a typical British comedy from the time but turned into something special by a tour-de-force performance, and one I've seen umpteen times since the late '60's. What an original the man was to me indeed, a Very Important Person.