Noel Coward collected people in the way that boys collect stamps; only with Coward they were rare stamps, in the finest condition. He was among the last of that generation of talents whose address books and holiday homes brimmed with people of equal gifts and even glossier reputations.

He lived in an age when fame fell like a warm cloak on to the shoulders of those who had dazzled theatre audiences, or readers of fiction, or cinemagoers, or art lovers. It was a time before celebrity had become a commodity that you settle for when you don't have enough talent for success.

The result is that Coward's correspondence — woven together into the skeleton of a biography by Barry Day in The Letters of Noël Coward — feels like a portrait of a vanished age. Letters and staccato telegrams zip around the world: to Marlene Dietrich and Lord Mountbatten; to Vivien Leigh, Alec Guinness and Virginia Woolf; to John Gielgud and Laurence Olivier; to Diana Cooper; to Edith Sitwell, William Somerset Maugham, Ian Fleming and Graham Greene.

Coward moved freely through an artistic Establishment (entry strictly on merit; although Coward shamelessly courted royals, too) that has largely evaporated like water dripped on a hot griddle. Look ahead 50 years and it's hard to imagine whose collected correspondence you might care to read, isn't it? Which of today's celebrities promises a passport into a similar world of artistic friendships and glamour? Tom Cruise? Britney Spears? Paris Hilton? James Blunt?

The range of Coward's friendships reflected the range of his talents. As his chum, Mountbatten, said at Coward's 70th birthday party at the Savoy: “There are probably greater painters than Noel, greater novelists than Noel, greater librettists, greater composers of music, greater singers, greater dancers, greater comedians, greater tragedians, greater stage producers, greater film directors, greater cabaret artists, greater TV stars. If there are, they are 12 different people. Only one man combined all 12 — the Master”.

You would sooner call Niagara Falls a cute water feature than Coward self-effacing. But when he sang: “I believe, that since my life began, the most I've had is just, a talent to amuse,” he betrayed a self-deprecation which camouflages his recognition of just how rare and precious is a talent to entertain. Coward made being amusing seem effortless. His version of Cole Porter's song Let's Do It must be the only instance of anybody at least matching Porter's mischievous humour as a lyricist.

Coward's circle spread far beyond Broadway and Shaftesbury Avenue. His weekly letters to the mother on whom he doted are his North, his South, his East and West. Here, too, is a gushing letter from Edith Sitwell, thanking Coward for sending her a copy of his Collected Short Stories (“There are no short stories written in England in our time that I admire more”). John Osborne writes: “I have always had the profoundest respect for you... You are a genius”.

Coward was won over by Harold Pinter's writing and backed a film of The Caretaker, cementing a bond between the two. Not that, even in the murky depths of kitchen-sink drama, Coward lost his appetite for showiness. When Lord Birkett, who produced The Caretaker, asked Coward for his address in Switzerland to send production updates, he replied: “Oh, just write, 'Noël Coward, Switzerland'.”

Even Virginia Woolf fell under his spell. After Coward wrote gushingly about Orlando, she replied that she felt “like a cat that is purring all over with pleasure at your praise and generosity.”

Their dizzy friendship waned a few years later when Woolf gave up her vague ambition to suck Coward into the Bloomsbury net and thereby, as she wrote in her diary, “save him from being as clever as a bag of ferrets and trivial as a perch of canaries”. Woolf failed to grasp just how rare, and how winning, such a combination was.

The Letters of Noel Coward, edited by Barry Day

Methuin Drama, £25

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