LONDON — The invitation to the memorial service for Vivienne Westwood came with a last specific command from the late designer herself: “When in doubt, dress up!”

The congregation at Southwark Cathedral on Thursday afternoon — the eve of London Fashion Week — had clearly taken those words to heart. Attendees spilled into the historic churchyard in white pinstripe bustiers, devil-horn tiaras and strings of statement pearls. Between majestic bouquets of purple heather, thistles and mimosa inspired by the Scottish Highlands, the pews heaved with splashes of bold Westwood tartan, embroidered bomber and biker jackets, PVC platforms, sequined tuxedos, slashes of colored eyeliner and oversize pink top hats.

Designers including Victoria Beckham, Paul Smith, Zandra Rhodes and Marc Jacobs arrived to pay tribute to Ms. Westwood, who died in December at 81. So, too, did the supermodel Kate Moss and the Vogue editors Anna Wintour and Edward Enninful. In other words, the great and the good of fashion royalty had come for a final farewell to the queen of British fashion, an anti-establishment, anticapitalist pioneer of punk who famously accepted her Order of the British Empire at Buckingham Palace in 1992 in a finely tailored dark gray skirt suit — and no knickers.

“How can I possibly chart the cultural impact of one of this country’s greatest designers?” the actress Helena Bonham Carter wondered from the pulpit. Her eulogy ranged from her first-ever purchase of a Vivienne Westwood item at age 15 (a white shirt from the designer’s Pirate collection and a matching cummerbund so she could look like Adam Ant) to the “obscene” amount of clothes she owned by Ms. Westwood (seven dresses in the Cocotte style alone), and included an anecdote about the time a reporter asked why she wore only Westwood on the red carpet.

“Because she’s a genius,” Ms. Bonham Carter recalled saying in response. “You have no idea how many ideas and choices have gone into everything she designs. She gives us instant body engineering with no lipo or diet.” She called Ms. Westwood “a true feminist and lover of women” who understood the power of protest and empowerment, channeled through both fashion design and a lifetime of activism.

“While Karl Lagerfeld tried to marry his cat, you drove a tank onto the prime minister’s front lawn as part of an anti-fracking protest,” she added, to laughter from the crowd. “Not many fashion designers do that.”

The service began with Abba’s “Slipping Through My Fingers” played by the Arnfield Brass, a band from northern England that rehearses less than a mile from the Derbyshire village of Tintwistle, where Ms. Westwood grew up. Celebrity friends like Chrissie Hynde and Nick Cave sang in honor of Ms. Westwood, while Gordon Swire, her brother, shared a moving series of video interviews he recorded of his sister before she died in which she recalled an incredibly happy childhood in the green rolling Derbyshire hills — where she is now buried and which she called “the most beautiful place in the world.”

Many family members spoke movingly about the designer’s life beyond fashion, including her husband, Andreas Kronthaler, a onetime student and longtime design partner, who described the moment he realized he would be with his “darling girl” forever (she was wearing, he recalled, a skintight chocolate-brown stretch cat suit and pink leopard jacket with trailing silk scarves for a Vienna museum trip), and her sons, Ben Westwood and Joseph Corré. Mr. Corré proudly described a mother who was “a wonderful teacher and freedom fighter” and wanted to change the world for the better, adding that she had left him with a very specific and rather ambitious to-do list from her deathbed in December: “Stop war, stop climate change and end capitalism.”

The memorial spanned the remarkable life of a self-taught iconoclast who changed contemporary conceptions of how clothing could be used to express — or rebel against — social and political norms and shape group identity. Little wonder that this season of London Fashion Week is being held in her honor. Ms. Westwood’s family has started a nonprofit, the Vivienne Foundation, that will focus on issues related to climate change, war, human rights and capitalism.

The final tribute of the service came from Cora Corré, Ms. Westwood’s granddaughter, who stood resplendent in her grandmother’s designs as she urged the crowd to continue honoring a legacy rooted in rebellion and questioning the status quo.

“We can only really touch on the characteristics of the phenomenon that is Vivienne Westwood: a grandmother, mother, sister and friend, a teacher, an artist and a designer,” Ms. Corré said. “It will never be enough.”