The summer of 1929 was the greatest London season since the first world war. There was a new Labour government under Ramsay MacDonald promising that the rule of the rich was over. Women under the age of 30 had the vote for the first time (the so-called flapper vote). But it was the antics of the aristocrats that filled the gossip columns, particularly their parties.

Fast cars, faster women and sexual experimentation: the parties got wilder. Drug abuse — particularly cocaine and hashish — was rife. Evelyn Waugh, embarking on his career as one of Britain’s finest writers, chronicled every excessive detail. He went to a lesbian party where a baronet “dressed first as a girl and then stark naked” danced the charleston while a Russian played a saw like a violin.

One account of the antics of the aristocracy provided a great comic set piece for Vile Bodies, his new novel. Lady Sibell and Lady Mary Lygon, sisters of Waugh’s friend Hugh Lygon, had been to a party in their white Norman Hartnell dresses and enjoyed a night’s dancing and drinking. When they returned to their London home off Belgrave Square, they found the door locked and the night footman fast asleep. But there was another family they knew well who had a night porter: the Baldwins.

At 10 Downing Street, the night porter woke the prime minister, Stanley Baldwin, and his wife. They came downstairs in their nightclothes, the PM in striped pyjamas, to be greeted by the Lygon girls seeking beds for the night. In the morning Baldwin rang Lord Beauchamp, their father, to ask if he would send a maid round with day clothes for the girls. “Balderdash and poppycock!” Beauchamp retorted and made them walk home in broad daylight in full evening dress.

Times Archive 1936 Mr. Hugh Lygon: an appreciation

It was quite impossible to know 'Hughie' Lygon and not love that smile and that indefinable charm which were his very own

• Death of Mr Hugh Lygon

• Lord Beauchamp: The Times obituary, 1938

• Brideshead Revisited: Book of the film of the book, 1981

In Waugh’s hands, their adventure was transmuted into a sublime comic episode where a wild flapper girl gatecrashes 10 Downing Street and appears for breakfast in her party clothes, to the incredulity of the prime minister and his wife.

Waugh’s relationship with the Lygons of Madresfield, the family’s ancestral home beneath the Malvern Hills in Worcestershire, provides a key to his inner world. Their house, which they and he affectionately called “Mad”, has often been described as “the real Brideshead”, an allusion to his most famous book. In many ways it was, provided we always retain defensive quotation marks around “real”.

After the summer of parties in 1929, the Lygons were overtaken by a scandal that reverberates through Brideshead Revisited. But this was not fiction; and it involved the King, a prince, a duke and a knight of the garter.

The Lygon girls’ father, the 7th Earl Beauchamp, was the perfect aristocrat, not only tall and handsome but also intelligent, cultured and highly artistic, an energetic and successful public figure and an exceptionally devoted father to his seven children. His family and their immediate entourage moved by private train between Madresfield, their Belgrave Square house and Walmer Castle in Kent, the earl’s official residence as warden of the Cinque Ports.

An ardent Anglo-Catholic, Beauchamp had shown a strong evangelistic streak at Oxford and had started to have the appearance of being a dangerously progressive radical. Later, however, he bore the sword of state at the coronation of George V, became lord lieutenant of Gloucestershire and served as lord steward of the royal household. By the time Waugh and other friends of Beauchamp’s children came under his spell in the late 1920s, he was the Liberal party’s leader in the House of Lords.

Did I hear him whisper to the butler ‘Je t’adore’?

Hugh Lygon, Beauchamp’s second son, met Waugh at Oxford where they were members of the Hypocrites’ Club, the centre of what would now be called the university’s gay scene. Although homosexuality was illegal, many senior members of the university actively encouraged it. According to A L Rowse, the don, Hugh Lygon and Waugh were lovers.

Hugh was admired for his floppy blond hair, his handsome face and his charming demeanour rather than his intellectual capacities. He was dashing but prone to melancholy and self-destructive drunkenness, which Waugh admired.

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy