The Black Sheep of Whitehall

The Black Sheep of Whitehall is a 1942 British blackandwhite comedy war film, directed by Will Hay and Basil Dearden, and starring Will Hay, John Mills and Basil Sydney. It was produced by Michael Balcon and Ealing Studios.

Davis is mistaken for the expert and gets involved in a series of interviews, giving answers based on gambling, con jobs, double entendres or just plain ignorance. These scenes are very funny and are made more so by the reactions of an increasingly incredulous Joss Ambler as government minister Sir John. Jessop later returns with Professor Davys and the confusion is sorted out, though it has left the BBC interviewers in a state of mental collapse. Jessop then discovers that the man he brought with him is in fact Crabtree Felix Aylmer, a member of a group of fifth columnists working for Nazi Germany.Jessop promises Davis a job if he will help him track down the real Professor Davys Henry Hewitt, who is being held in a safe house by Crabtrees associates. Assuming a number of disguises, Davis and Jessop set off to foil the plot before the treaty is compromised. ........

Source: Wikipedia