Q Planes

... instead it is a fun little espionage piece with a witty script with its tongue placed firmly in its cheek. Set during the tense years preceding the outbreak of WWII, the Brits are losing experimental aircraft (the titular Q Planes) in mysterious circumstances, and Ralph Richardson's character is head of a government agency out to discover whats really going on, whilst Valerie Hobson is seemingly a spy for a foreign power, trying none-too-subtly to extract information from a bemused, cynical test pilot played by Laurence Olivier just before he headed off to bigger things.

The tone of the film is set from the initial scene, which opens with a composed, but confused Richardson trying to work out what he's doing in a trashed room, why he's surrounded by police, and what the heck his own name is.

Aside from a fun plot & great cast, there are some neat period aircraft up for viewing, for those with an interest in such things. Some other interesting tidbits that Wikipedia turned up are that airfield shots in the film were filmed at Brooklands (an early center of aviation & motor racing) and that the film was apparently based off actual events where the British government believed that the Germans were behind the downing of an experimental plane over the English Channel, so they helped fund this movie to let the Germans know that they were on to them, without any messy diplomatic unpleasantness being needed.