A comet streaked into France in the 1930s, its fallout sending the staid echelons of haute couture into a tailspin. A mere 30 years later a rogue missile blasted into London, blowing dainty English clothes sense to smithereens. Both these thunderbolts shot the stuffing out of cloying conventionality, one with an arrow-narrow silhouette, the other by blitzing the luxe out of luxury, the ex out of exclusivity.

It’s worth studying the photographs of those two alien invaders, the subjects of these lengthy works. The young Elsa Schiaparelli, sleek-headed, confident, wearing strict black: and the young Vivienne Westwood, with tousled hair and a workaday high-street suit: both have intense dark eyes with a far-reaching gaze above their determined mouths — ambitious egos, sisters perhaps, but over, not under, the skin.

‘Comet’ was the word Janet Flanner used in the 1930s to describe the arrival in France of the Italian aristocrat Schiaparelli. Secrest has enlarged on Flanner’s diamond-etched essay, and trawled Elsa’s autobiography Shocking Life, a matter-of-factly written work in which she rather weirdly refers to herself alternately in the first and third person.

Derbyshire-born Vivienne Isabel Swire’s autobiography (her second, by the way, this one assisted by Ian Kelly), chronicles her slow rise from the village of Tintwhistle to punk grande dame, and takes the sledgehammer approach, resolutely in the first person. And boy has Vivienne got a lot to say — some of it defiantly honest, much of it on-trend guff. Rumours are swirling with accusations of plagiarism — about passages being lifted from another author; those parts may account for the book’s pavement-slab weight.

There are comparisons to be made. They both benefited from muses, Salvador Dalí, among others, encouraging Schiaparelli to adorn her streamlined Chanel-rivalling, collections with unlikely motifs such as lobsters, frilled lamb cutlets and his signature chests of drawers; while Westwood’s one-time husband Malcolm McLaren insisted on more subversive images with knobs on. Remember those cock-kissing cowboys, the exhortations to destroy, the safety-pin-lipped Queen, the S&M and the nostalgie de la boob T-shirts printed with disembodied breasts?

The difference is that Schiaparelli — let’s call her Schiap, as she herself, her friends and contemporaries did — definitely influenced future fashion, particularly in Hollywood, where couturiers such as Travis Banton, Omar Khyam and Adrian were quick to pick up on her fluid, figure-skimming lines, backless dresses, re-working of furs and feathers, wide padded shoulders and oversized jewellery. For the best confirmation of her cinematic impact one only has to watch ‘There’s Beauty Everywhere’, the last segment of Vincente Minnelli’s Ziegfeld Follies, a Dali-esque number in which Katharine Grayson sings in clouds of shocking pink soap bubbles, while behind her, on a painted desert, receding rows of chorus girls in Schiap-inspired satin sway surreally in a wind-machine created gale.

Westwood, however, was primarily, and self-confessedly, inspired by Hollywood, from James Dean’s grunge to Errol Flynn’s piratical swashbuckles. While Schiap looked determinedly forward, Westwood, with her bookworm bent, delved into and delivered witty, updated versions of les Incroyables, with crinolines and dirndls, and of course the corsets and bondage from which Schiap had so assiduously freed the female form.

There the comparisons end. Westwood, blessed with a stable childhood, clearly has a loving, caring nature and is able to draw the strands of her various relationships into an extended happy family, with hardly a bad word for anyone — with the exception of McLaren. Her well-publicised outrageous persona and opinions tend to belie her intellectuality, her knowledge of history, familiarity with the classics and her deep-seated social scepticism.

Schiap, on the other hand, had hardness in her ambition and a streak of cruelty, especially in her treatment of her polio-damaged daughter Gogo. She lived and worked and triumphed in that interwar period of gilded, globe-trotting art-and-café society, but one senses an underlying personal dissatisfaction. Her amorous relationships (and I was fascinated to discover we shared a lover) were haphazard, short and unsatisfying, though her friendships with women, particularly the dazzlingly beautiful and brilliant, but sadly unpublished, diarist Bettina Bergery, lasted till her death.

Meryle Secrest, who has written trenchant, admirable biographies of Bernard Berenson, Leonard Bernstein and Modigliani, chronicles the intercontinental, party-giving, flippant (until Hitler came along) life of Schiap’s Paris/New York/Los Angeles axis. The work and the dresses are described in intricate detail, though the prose sometimes lapses into Bunty-style exclamations: ‘Even today — for a formal afternoon reception — the quintessence of chic!’; ‘How could one resist?’ and ‘It couldn’t be prettier!’ Ian Kelly’s interview technique is more wham, bam, thank you Dame. Though only three decades separate these two women, it’s certain that they created fashions that startled their generations. But while Schiaparelli’s most enduring legacy is ‘shocking pink’, Westwood’s endearing punk is shocking to this day.