London's circular fashion start-ups are reshaping the industry while struggling to integrate with the city's broader sustainability goals. Through three innovative businesses—a clothing swap platform, a repair-and-remake retailer, and a rental service—we uncover the dissonance between start-up innovation and urban infrastructure. While these companies create impressive circular models at the enterprise level, their impact remains constrained by fragmented city systems. With these practical strategies, entrepreneurs can position their businesses within London's urban metabolism, creating value for both shareholders and the city. For policymakers, it outlines key interventions to bridge this gap and accelerate London's transition to a truly circular ecosystem.