Yes, Peter Ustinov and Maggie Smith are lovable creatures, but that's where the charm ends for this movie. The rest of the casting is inexplicable -- Why are the other 2 major roles cast with Americans Karl Malden and Bob Newhart? Their positions as executives in a British firm make no sense. Bob Newhart is particularly disappointing, as none of his inherent humorousness is on display. Caesar Romero makes what amounts to a cameo appearance, and would have lent this movie more interest with a bigger role. The computer hacking portion of the plot is not ahead of its time, but rather makes no sense and is impenetrable even by 1968 standards. The implausibility of Ustinov's instant education is just the beginning of a string of ruinously mishandled plot mechanics related to the technical aspects of the story. But they do save the worst for last, where Smith pulls a deus ex machina to resolve a lost plot that never warranted being found in the first place.
If you want a quirky British ex-convict caper story from the era that works, try The Italian Job.
If you want a quirky British ex-convict caper story from the era that works, try The Italian Job.