According to Mr.David Fletcher from the Bovington Tank Museum, Tom Lakeman, the designer of the AA mount installed on numerous British tanks of the early war years, was a Royal Tank Regiment officer, slightly mad according to people who knew him, who devised all kinds of strange machine-gun mountings.
The principle was a balance of arms and springs, like an office desk lamp, the idea being to reduce the weight of the weapon when used against aircraft.
In practice they were usually more trouble than they were worth and most soldiers hated them and tried to throw them away at the first opportunity.