Tom Fletcher CMG was foreign policy spin doctor to Tony Blair, Gordon Brown and David Cameron between 2007 and 2011 before becoming British ambassador to Lebanon, where he served until 2015. ‘I’ve learned a huge amount from this job,’ he writes. ‘If I’m honest, I’m completely knackered. It’s been a demanding posting.’

Fletcher has since left the diplomatic service but is conducting a major review of British overseas policy for the Foreign Office. He is a fully wired moderniser trapped within a hierarchical and traditionally minded public service. His book has some sensible suggestions, though no cliché is left untouched, and the enthusiastic tone is of a desperately right-on vicar: a Giles Fraser of King Charles Street. Fletcher donated blood after an attack on the Iranian embassy in Beirut and released a photo of himself with a needle in his arm on Twitter, being gratified when President Rouhani and hundreds of other Iranians retweeted it. That’s the spirit of the book.

His amiably engaging but lightweight book begins with a potted history of diplomacy, a concept derived from the ancient Greek word for a folded paper. Over the course of a hundred pages he deftly paints the main privileges of the caste. Genghis Khan introduced diplomatic immunity and the diplomatic passport.