There’s a photograph of Jordan Mooney, standing outside the clothes shop Sex, that perfectly encapsulates her extraordinary impact. Sex was Malcolm McLaren and Vivienne Westwood’s London boutique, which sold their designs along with fetishwear. It is also where in-house band the Sex Pistols were incubated.

Jordan was more than a shop assistant: she was the embodiment of the Sex aesthetic. In the picture, she’s rocking a peroxide beehive, with a leotard, fishnet stockings and a sulky bombshell attitude – stopping a passing businessman in his tracks. The look on his face says it all: in 1976, the sight of someone like Jordan was astonishing.

“Men were confused by me,” she says today. “They would wolf-whistle, shout all kinds of things, even offer me money, because they didn’t understand why I looked like I did. I was running a gauntlet every day. People were scared of me. And the funny thing is, I was actually quite shy.”

Born Pamela Rooke in Seaford, a coastal town in East Sussex, Jordan wore jaw-dropping outfits and savage makeup, all of which made her the first face of punk. Only 19, she would leave the house wearing rubber knickers and stilettos, or sheer skirts without underwear – deconstructing her clothes to her own incendiary design. It made the daily commute on British Rail, from Sussex to Chelsea, a drama in its own right. “Some of the things I wore were quite near the knuckle,” she says. “People were apoplectic with rage. I had to be moved into first class for my own safety.”

Sex bombs: (l-r) Steve Jones, regular customer Danielle, Alan Jones, Chrissie Hynde, Jordan and Vivienne Westwood pose at the shop in 1976. Photograph: David Dagley/Rex

Long before punk went mainstream, Jordan was tearing up the rulebook, forging an identity the world would later follow. She took her cues from the 1950s – leather pencil skirts, dominatrix heels – and added her own touches of mayhem. Derek Jarman, who cast her in Jubilee, described the racoon-eyed rebel as “the original Sex Pistol”. Nobody looked like Jordan, or would even dare. She was defiantly original, both terrifying and seductive.

Aware of her value, McLaren urged her to get up to mischief wherever the Pistols played. Whether crashing around on stage, baring her breasts or simply adding visual impact with her Mondrian-inspired makeup and vertiginous hair, Jordan soon became synonymous with the band’s “we don’t care” attitude. She put the sex into the Sex Pistols.

Normality saved my life … Jordan now works as a veterinary nurse. Photograph: Alan Powdrill/The Guardian

Defying Gravity, her candid new memoir, follows punk’s rapid rise and fall, as well as her own evolution from keen ballet student to the Boudicca of new wave. It’s the poignant tale of a small-town girl who dared to be different. “My mother wanted a girly kind of girl and that was never going to happen,” she says. “She absolutely hated the way I looked and would walk several yards behind me on the street. I regret the anguish I caused.”

Why Jordan decided not merely to be different, but to cause chaos with her appearance remains largely unexplained by the book. “Ballet taught me a lot of things: how to be strict with myself, how to work through pain,” she says. “It taught me how to dress up and express myself. I didn’t want to be scripted. I wanted to live my life in an impromptu and spontaneous way.”

When she applied for a job at Sex, clad in nothing but sheer black tights and a belted mac, Westwood hired her on the spot. “I’m not particularly fond of the word muse, because I think we were a bit more of a team really,” Jordan says. “We tried to present a feeling that the shop was a place that, if you had the guts to walk in, you could just hang out. Like the coffee shops of the 1950s, or the cafes of Prague, where philosophers would go to chew things over.” Amid leather gimp masks, of course.

As the ground zero of a musical revolution, Sex has gone down in history. Pistols bassist Glen Matlock was the Saturday sales assistant, while drummer Paul Cook and light-fingered guitarist Steve Jones would frequent the premises, drawn to its subversive charms and easy pickings. When John Lydon (AKA Johny Rotten) auditioned, screeching along to the shop’s jukebox, punk had found its HQ.

Jordan remains the Sex Pistols’ most ardent fan. “What I loved, especially in the early days, was that they were so unscripted. But then I witnessed the unravelling of Sid – and it hurt. I couldn’t watch [the 1986 film] Sid and Nancy for years. Can you imagine? A really good friend and suddenly they’re dead. Drugs, murder, lurid headlines. What a nightmare.”

Adam Ant and Jordan bring punk to the premiere of Saturday Night Fever in 1978. Photograph: PA

The demise of punk, a few ill-fated attempts to manage bands, plus a marriage that fell apart, all took their toll. Escaping London in the mid-80s, Jordan returned to the coast and reinvented herself in the most un-punk fashion. “I trained as a veterinary nurse and began breeding cats. Things had become too hectic. It sounds really corny, but normality saved my life.”

She is, however, still a punk at heart, leather-clad with burgundy hair. “I will always wear my Tits T-shirt,” she says. “I fill it out very nicely.”

• Defying Gravity: Jordan’s Story is published by Omnibus Press on 2 May.