BRIAN VINER: There's no-one like Twiggy - her new biopic reminds us how she broke the fashion mould without ever losing herself

There were mononymous female stars before Twiggy .

Cher , for example, was already famous by the time Nellie and Norman Hornby's youngest daughter Lesley was reinvented as Twiggy in 1966.

And there have been many since, such as Madonna , Adele and Beyonce .

But none of those other single names evoke a time and a place – London in the Swinging Sixties – as powerfully as Twiggy does.

And by far the most absorbing part of Sadie Frost 's thoroughly enjoyable if rather gushing documentary, which had its world premiere last night (THU) at the London Film Festival, concerns those remarkable years.

In 1966, in the course of a few dizzying weeks, young Lesley went in her own words from being a 'shy, introspective' schoolgirl to one of the most recognisable people on earth.

Within a few more years she was famous enough to be a David Bowie lyric, in his song Drive-In Saturday.

Frost's previous documentary was about the designer Mary Quant, another woman synonymous with the Sixties.

But, as cultural icons go, even the redoubtable Quant was quickly eclipsed by the working-class teenager from Neasden in North-West London.

It all started with a haircut.

Looking for shampoo, 16-year-old Lesley popped into a posh Mayfair salon, House of Leonard, where Leonard himself spotted her and asked if she'd mind modelling his new pixie cut.

The cropping and bleaching took seven hours.

She was then packed off to have photographs taken, the fashion editor of the Daily Express noticed them, and her life changed.

She acquired a new name and was hailed as 'The Face of '66'.

Other celebrated models of the era pop up in the film to recall what happened next, as Twiggy's boyish 31-23-32 figure and her 'gender-fluid little elfin face', as Joanna Lumley puts it, made her the world's pre-eminent supermodel.

What didn't happen next, even at the height on both sides of the Atlantic of so-called Twiggy-mania, was any hint of big-headedness.

The cut-glass vowels of Lumley and another contributor, Pattie Boyd, highlight how unusual it then was for a model to talk like Twiggy did.

But as Paul McCartney points out, her blue-collar roots kept her grounded. 'What you saw was what you got,' he says.

Not to mention what you heard. Another friend, Dustin Hoffman, fondly recalls her 'truck-driver's laugh'.

Twiggy herself, still beautiful at 75 and as engagingly down-to-earth as ever, delivers her own recollections throughout.

She politely remembers Justin de Villeneuve, her boyfriend and manager in those early years, who did become too big for his trendy boots and was duly kicked into touch.

And she describes a bizarre episode when she and her first husband, American actor Michael Witney, father of her only child Carly, were summoned for an audience in Los Angeles with the record producer Phil Spector.

They fled when he pulled a gun on them.

By then Twiggy had forged a secondary career as a (surprisingly good) singer, while the director Ken Russell had spotted and nurtured her acting promise.

In 1981 she was an acclaimed Eliza Dolittle in a TV version of Pygmalion, and while everyone knew she could nail the Cockney 'sparrer', she was just as convincing as the refined, ladylike version of Eliza.

The appealing paradox of Twiggy is that for all her impressive versatility, she has never changed.

She is completely, authentically herself, in a business in which not that many are. Nor, despite a painful marriage break-up (Witney was an alcoholic, who died of a heart-attack aged 52), does she appear to have any skeletons in her closet.

That might not make her the most compelling subject for a documentary were it not for everything else in her closet: the clothes, the ineffable style, the indelible images.

Frost's film becomes steadily less interesting as she turns her gaze to the older Twiggy as the saviour of Marks & Spencer, the honour of being made a Dame in 2019, and her seemingly blissful 36-year marriage to the English actor and director Leigh Lawson.

But if only for the way it chronicles those tumultuous early years, it is a treat.