Back in 1612, a genial British diplomat, Sir Henry Wotton, got into trouble for defining an ambassador as an honest man who is sent abroad to lie for his country. Wotton’s protestation to the furious King James I that the word ‘lie’ meant merely ‘to reside’ fell on deaf ears. It was two years before the unlucky diplomat received a new posting.

Pondering in his introduction to this wonderfully learned, gossipy and instructive book how far Wotton’s playful statement reflects reality, James Stourton notes that diplomats today still have to be economical with the truth. They must express limitless woe at leaving a post, even if the posting were to somewhere less spectacular than Pauline Bonaparte’s erstwhile palace in Paris or the exquisite homage to Hawksmoor that Edward Lutyens created for the British ambassador in Washington. They must then profess their unalloyed delight at taking up residence in, let’s say, Kabul. But each posting carries its own risks. A mission to Paris often still requires – as one witty diplomat observed – a conscientious ambassador to lay down his liver for his country. At Kabul, where no family members are permitted to join the resident within his secure compound, a crash course in commando-style defence technique forms a mandatory part of each new ambassador’s training.

Back in Wotton’s day, courtier diplomats were expected to buy their own homes abroad. Only in 1799, at Lord Elgin’s request, was a plot of land granted in Constantinople for the building of the first British embassy abroad. By the 1870s, the need to protect the borders of India from Russian encroachments and defend Britain’s trade routes to the East led Queen Victoria’s government to emphasise the long reach of her jewelled grasp. Embassies arose in Gibraltar, Kuwait, New Delhi, Tehran, Cairo, Addis Ababa and Singapore. Their purpose, lightly masked by elegant hybrid architecture, was to sound forth the trumpet of British superiority.

Today, those same elegant embassies offer a stark contrast to Britain’s diminished power, the waning of which Stourton traces back to Suez. But Stourton is an optimist. These glorious buildings still represent power. Perhaps, he suggests, Brexit’s unforeseeable results will bring them back into play. Even today, apparently, the most elusive of French officials will respond to an invitation to that earthly paradise, the British embassy in Paris. One of Luke White’s photographs captures the most endearing corner of state life in this grandest of all the embassies: Duff Cooper’s addition of a cosy library to Pauline Bonaparte’s lavish enfilades. Cooper’s wife, Diana, meanwhile offered a witty nod to her French predecessor by creating a bathroom in the style of Napoleon’s campaign tents.

Admirable as a guide, his sharp eye picking up on details like the fact that the previous British embassy in Moscow offers the city’s best – and indeed only – view into the spider’s web of the Kremlin, Stourton maintains an enjoyably irreverent line on the furnishing of these quasi-palaces. He’s rightly enchanted by the Byronic touches enhancing the embassy in Athens (formerly the home of President Venizelos). But the dining room of the embassy in Buenos Aires is briskly dismissed as ‘pure Pall Mall’, while Kabul’s most recent refurbishment is snappily described as a mix of ‘Ikea and Land of Leather’. It’s possible to detect the ghost of a grin behind Stourton’s demure description of a majestic statue of Queen Victoria that still dominates the entrance to the embassy in Bangkok. Nineteenth-century Thailand revered the distant empress. Although Victoria continues to guard the way to her enclave in Bangkok, she now also fulfils the role of a hefty fertility goddess, family-minded couples filling her lap to capacity each day with blossoms and bouquets.

While some might dismiss it as a gorgeous, oversized picture book garlanded with snippets of text, British Embassies is important enough to merit publication in a smaller and less image-driven format. The historical research is formidable. The focus is on how each diplomat contributed to his (female diplomats arrived shamefully late on the scene) dual purpose: namely, advancing the interests of Britain and winning support for British policy. Excellent on the lead-up to the First World War (two telegrams are published here for the first time, showing how Sir Maurice de Bunsen, out in Vienna, was the first to predict what would follow on from the assassinations in Sarajevo), Stourton is just as good at describing the delicate role performed in the 1970s by Sir Anthony Parsons, out in Tehran, in seeking to stay close to an increasingly isolated Shah. The dreamily beautiful embassy in Iran, Stourton points out, had once hosted the most remarkable social occasion ever to grace a diplomatic residence: the 69th-birthday dinner for Winston Churchill, at which Britain’s wartime prime minister sat between Roosevelt and Stalin as they carved up the spoils of war.

Spine-chilling as his account of the risk involved in becoming Her Majesty’s representative in Kabul is, Stourton excels in the touches of levity that make his book so entertaining. In Kabul every Boxing Day, an egg-and-spoon race takes place on the embassy lawn. Interned in the Tokyo embassy from 1940 to 1942, bored British citizens took up flower-arranging and writing operettas. Questioned on a later occasion about his right to stand in a position normally occupied by the Queen during a formal line-up, HM’s ambassador to Japan briskly announced, ‘I am the Queen.’ End of argument.

Witty, informative and endlessly fascinating, this is a splendid addition to Stourton’s stable of books about grand houses. Let’s hope it finds a more manageable format for a second edition.