The memorial service started promptly at 11 a.m. after a crowd of onlookers had gathered outside behind police barricades to watch the parade of arriving celebrities and fashion-world figures, many of them in town for London Fashion Week.

Inside the cathedral, two choirs led a clerical procession past Mr. McQueen’s family members on one side and his friends and colleagues on the other, seated in a facing semicircle. They included the designers Stella McCartney and Hussein Chalayan; the actress Sarah Jessica Parker; the models Naomi Campbell and Kate Moss; and the heiress and couture collector Daphne Guinness, who was somberly outfitted in McQueen tailoring with a black feather-shaped hat.

Image Anna Wintour, the editor of Vogue, said in an address, “There was no comfort zone with Alexander McQueen.” Credit... Sang Tan/Associated Press

In his opening address, the Rev. Canon Giles Fraser acknowledged the two distinct spheres of influence on the designer.

“When he needed support and solace, he found it in his family,” Mr. Fraser said. “Which is why, despite the dazzle of his world, he never forgot his East End roots.”