The evil genius of David Cameron’s EU referendum ploy was summed up in a single sentence of his speech this week outlining the alleged threat to Britain’s national security from a vote for Brexit.

Mr Cameron set out the conundrum facing voters as follows: “If you were buying a house or a car, you wouldn’t do it without insisting on seeing what was being offered, and making sure it wasn’t going to fall apart the moment you took possession of it.”

Indeed you wouldn’t, except that in the case of Mr Cameron’s EU referendum, checking under the bonnet or commissioning a full structural survey of the implications of a Brexit vote is impossible - and designedly so.