On July 13, 2026, a new U.K. short selling regime entered into force, replacing the U.K. version of Regulation (EU) No. 236/2012 on short selling and certain aspects of credit default swaps, which had been assimilated into U.K. law following the U.K.’s withdrawal from the E.U. (UK SSR 2012). The new regime is composed of the Short Selling Regulations 2025 (SI 2025/29), issued by HM Treasury on January 13, 2025, and a new Short Selling Rules sourcebook within the Financial Conduct Authority (FCA) Handbook (FCA SSR). The SSR 2025 establishes the legislative framework for the regulation of short selling and confers rulemaking, supervisory and enforcement powers on the FCA. The FCA SSR sets out the firm-facing requirements, consolidating provisions previously contained in the U.K. SSR 2012, related delegated regulations, associated technical standards and relevant European Securities and Markets Authority guidance, including its Q&A. This guest article by Sidley Austin attorneys Leonard Ng and Qalid Mohamed addresses the scope and principal requirements of the new regime; compares the U.K. and E.U. short selling regimes; and considers its implications for hedge fund managers. For additional insights from Ng, see “A U.S. Fund Manager’s Perspective on AIFMD 2.0” (Mar. 26, 2026); and “FCA ‘Dear CEO’ Letter Highlights Focus on Private Markets and Resilience” (Apr. 10, 2025).