BETH DITTO was livid. Topshop, the fast-fashion chain, had approached Ms. Ditto, the outsize lead singer with the punk band Gossip, and a favorite mascot of the fashion world, to perform at its flagship store in London. Blowups of her heart-shaped face and rotund form would be on display.

But Ms. Ditto, who happily flaunts what the British like to call her “wobbly bits,” was having none of it. “I don’t think it’s fair to put my face somewhere where they would never let me in there to wear their clothes,” she complained on a blog. If the chain hoped to capitalize on her grooviness, she wrote, why not accord her the same status it does Kate Moss, and let her create a “big girl” line for Topshop.

“Give me the job,” Ms. Ditto demanded. “I want to design.”

Her message, flung down like a gauntlet, reached the ears of the Arcadia Group, the parent company of Topshop. This month, a couple of years after Ms. Ditto’s sound off, Arcadia plans to unveil a collection that Ms. Ditto designed for Evans, the company’s plus-size division. Available in the United States on the Web, it highlights cutting-edge looks like a corset dress and a cropped biker jacket.