The result is Fashioning The Beatles: The Looks that Shook the World, a book that examines the profound impact the Beatles had not just on pop culture over the decades, but how the way they dressed has inspired people ever since.

“Their clothing became their biography,” says Kelly. “It mirrored their artistic evolution and the maverick spirit of this brand, their curiosity, their no-bullshit approach to life, to culture, to music. They were very astute and ambitious guys, they surveyed the competition, they determined at the start, they weren’t going to be like anybody else.”

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As the book tells their story, the world-conquering quartet first really connected because they loved the way one another looked.

“The whole point is, there really wouldn’t be any Beatles if they didn’t jive on each other’s looks first,” she says. “That’s how they got together. They couldn’t really play or read music. But when Paul [McCartney] first laid eyes on John [Lennon] and Ringo [Starr], he thought, ‘I like that cool-guy look.’

“It was a little menacing. They were all about the clothing, and each one innately had a connection to style and fashion. All throughout their career together, they influenced each other with their clothing. They wore each other’s clothes. They wanted to dress alike. They wanted to have that bond of fashion.”

The opening of the book is rooted in 1967, the day before The Beatles unveiled their Sgt. Pepper’s Lonely Hearts Club Band, arriving at an outdoor photo session in London’s Hyde Park “colourfully and eclectically dressed”.

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“Each Beatle was attired for the occasion with mismatched articles of clothing, combinations of made-to-measure and mass-produced. Together they reflected every hue of the rainbow,” she writes. “The Beatles burst on the eye like gilded butterflies in a grey landscape, heralding the arrival of the Summer of Love and their ascendancies to a new pinnacle of international pop culture stardom.”

Thereafter, the book is arrayed in chronological order, starting with 1960 (a chapter called “Tough Leather”), through to their much-copied Nehru jacket look of 1963 (“Uncollared”). “The collarless suit became an overnight sartorial hit,” says Kelly. “But by then they were off it, and onto the next thing. They always wanted to be different, to stand out on their own terms.”

A subsequent chapter examines the boys’ fascination with all things vintage, (“Raging Retro”, chronicling 1967) and concludes in 1970 with “Beyond: Slouching Towards Immortality”. Each chapter is anchored by a fashion-related quote from one of the boys – in “Tough Leather”, she cites George Harrison as saying, “That outfit of mine was very risky,” and in 1961’s “Cosmetic Conversion” Lennon opines, “We had to wear suits to get on TV. We had to compromise.”

The choice to go year by year was a considered one, she says.

“It allowed me to take a deep dive into the clothing choices made by the group – why did they do that, where did it come from, what were the politics, what was happening in society. It allowed me to go on this incredible voyage of discovery, and to see that this was the perfect time for that group. Fashion and the Beatles all happened at once.”

The group played its last public concert together in 1966, in San Francisco – almost four years before announcing its split in April 1970 – but the astonishing breadth of looks they became known for have permeated the zeitgeist ever since.

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Tony Palmer, who directed the 1968 movie All My Loving, about The Beatles’ era in British popular music, penned the preface to Fashioning.

“Yes, the haircuts; yes, the suits; yes the paisleys, the Nehru collars and the tight trousers,” he says by way of introduction. “They were innately stylish young men who, by constantly changing their appearance (mostly to please themselves) altered the look of a generation, not once but time and time again. Why? Because they were original. They did not follow fashion. They took it in new directions, becoming the leading style makers of their day.”