The US passport revelation leaves an intriguing question floating in the air. Could Johnson be prime minister and then US president? He was born in New York and is thus a "natural-born citizen", a constitutional requirement for any presidential candidate. He told David Letterman in 2012 that he could "technically speaking" be US president. In Johnson's 2006 Spectator piece he wrote: "When the going has got tough in England it has sometimes crossed my mind that I could yet activate the Schwarzenegger option and flee to the land of opportunity, perhaps beginning as a short-order chef in Miami before winding up as Colorado senator and, inevitably, president." Tongue was firmly in cheek. Or was it?