“Pretty, spirited, exuberantly self-confident”, Barbara Ker-Seymer was the archetypal flapper, bounding about Mayfair dolled up in a sailor suit. She was known as Bar, although she also answered to Bubbles, Old Tart and Tottie, and her life in the 1920s was a round of nightclubs, fancy-dress parties, coming-out balls and “intimate lunches”. If, during these cavortings, a man pounced, “Bar immediately drew out her hat pin and stabbed him in the hand”.

Her tastes, in any event, tended more towards the sapphic, although as Sarah Knights reminds us, these were unfriendly times for lesbians. One crusty MP, Lieutenant Colonel Moore-Brabazon, argued in Parliament in 1921 that “lesbians had abnormal brains and should be locked up as lunatics or hanged”.

Bar’s claim on modern attention, according to Knights, is that she was a first-class social photographer who was “exceptionally skillful in manipulating light, bringing a sculptural quality to her subjects”. They included Oswald Mosley, Nancy Cunard, Elizabeth Bowen and Evelyn Waugh. Indeed, it is the generation of Waugh’s Bright Young Things whom Bar represented — the Jazz Age silliness, which followed naturally from the horrors of the First World War in the same way that the Goons were a release valve after the Second World War.

This thoroughly entertaining book, therefore, celebrates people “united by a mutual sense of humor and a love of films, fashion, art, theater, ballet, blues and jazz”. Incidentally, Bar’s chief recollection of the First World War was that of recuperating veterans pinching her bottom at a sing-along at her grandmother’s house.

She was known as Bar, although she also answered to Bubbles, Old Tart and Tottie, and her life in the 1920s was a round of nightclubs, fancy-dress parties, coming-out balls and “intimate lunches.”

Bar, born in 1905, was lucky to be supported by substantial legacies from maiden aunts who paid for cameras and her flat in Fitzroy Square. At least at first, there was plenty of family money, derived from agricultural fertilizer, funding an estate in Dorset and a stucco mansion in Knightsbridge. Her paternal grandmother wrote racing novels, was a friend of Edward VII and was the dedicatee of Arthur Sullivan’s tune for Onward, Christian Soldiers. Her maternal grandfather was painted as a child by Frederic Leighton; despite siring five children, he “was almost certainly homosexual”, having a long liaison with the Earl of Carlisle.

Bar’s father, Vere, was required to make a living after his father announced that “a severe financial crisis had fallen upon the family”. “A string of bad bets at Newmarket” were in part to blame. Vere set sail to Argentina with the equivalent of just over $5,000 to make a fortune; alas, he inherited his father’s itch to gamble. He only got as far as Lisbon, having squandered every penny on shipboard poker.

Anthony Powell put Vere in a novel as Mr Nunnery, who “first appears as a moustachioed drunk in a dinner jacket”. Declared bankrupt in 1912, he was “not averse to battening on wealthy friends” with whom he would go hot-air ballooning. Although he would rob Bar’s money box to pay for taxis, the feckless Vere is hard to dislike — when Bar was stripped of her prefectship at school for singing the “Mee-ow Fox-trot” jazz song, he told her: “High spirits are no crime, altho’ few people are wise enough to know that they are a virtue.”

Bar’s mother, Diana, was less of a good egg. She took recourse in Christian Science and took up with another respectably married woman, Mrs Haworth Booth. Because of her Christian Science beliefs, which meant an aversion to the medical profession, Diana’s principled neglect left Bar to suffer long bouts of tonsillitis and untreated ear abscesses, which were left to burst of their own accord. Bar’s stone deafness grew worse.

Bar attended the Chelsea College of Arts, where her bosom companions, with whom she was out to have fun, were Billy Chappell, a ballet dancer and musical director, Edward Burra, the painter, and Frederick Ashton, the choreographer, who would chuck at the last minute if a better engagement was on offer, typically from royalty. Knights expertly evokes this hedonistic period, when hostesses liked “dragging people upstairs and putting them on top of each other”. There is a cameo appearance from David “Bunny” Garnett, the subject of Knights’s previous superlative biography, Bloomsbury’s Outsider, who is glimpsed fornicating on the hats and coats at one party.

It is the generation of Evelyn Waugh’s Bright Young Things whom Bar represented — the Jazz Age silliness, which followed naturally from the horrors of the First World War in the same way that the Goons were a release valve after the Second World War.

Bar got into the photography business by recording these parties for the gossip columns. We are told she had a knack for chiaroscuro, retouching and cropping and could create distorted shadows reminiscent of German silent films. Using a Rolleiflex, Bar brought to photography “her knowledge of life-drawing, portraiture and art history”. Her studio was in Grafton Street, above Asprey’s the jeweler, and her work grew to be admired by Paul Nash, Man Ray and Jean Cocteau, although the latter was befuddled by opium.

Then, abruptly, it was over. Bar’s livelihood disappeared during the Second World War, when photographic materials were hard to find and paper was rationed. Worse, Bar lost her negatives, and images of hers that survived were — and still are — misattributed to Cecil Beaton because, Knights argues, “it was assumed that no other British photographer of the 1930s could attain such heights of artistry, glamour and sophistication”.

Bar didn’t repine. Although she had been brought up by her mother “never to depend on a man”, in 1941 she married Humphrey Pease, who liked to dress up in a skirt and receive “chastisement” from his partner, who had to be garbed as a prison wardress. Bar was also expected to dress up as a nanny and tell Master Humphrey it was bathtime. They were divorced within a year.

In 1945 Bar married an intelligence officer called John Rhodes, who invited his mother on the honeymoon. A child, Max, was born, to whom Bar was devoted. Rhodes, however, deserted his family and never paid any maintenance, so Bar worked in a café, making waffles for Americans. She then decided to open a chain of coin-operated launderettes and became a successful businesswoman, buying freeholds around London, finding she was good at maintaining financial ledgers and applying herself to cashflow and marketing.

She kept up links with bohemia by befriending Patricia Highsmith (“quarreling with Pat would be like quarreling with a dog with rabies,” Bar once said) and the jolly artist Beryl Cook, who put Bar in several of her works. Burra stayed with Bar in Islington, North London, when visiting weekly from Rye. Spectacularly drunk, he was always having to be scooped from gutters. Ill with anemia, jaundice and rheumatoid arthritis, Burra described himself as “a derelict meths drinker on the way to the crypt”.

With the best will in the world, Barbara Ker-Seymer was never an important figure, or an unjustly neglected one, so Knights is right to expand this biography to take in other personalities — Chappell, who worked with Laurence Olivier and Orson Welles; Ashton, who was born and brought up in Ecuador; and, of course, Burra, whose surreal canvases command more attention now. Bar, who died peacefully in 1993, aged 88, was a good listener and easy with her charms with the various characters she met. Where would we be without such well-meaning sorts?

Roger Lewis is a critic and the author of Seasonal Suicide Notes and What Am I Still Doing Here?