Sir William James Lynton Blair (born 31 March 1950) is a British retired judge. He was previously a Queen's Counsel at London barristers' chambers 3 Verulam Buildings, specialising in domestic and international banking and finance law. He is the elder brother of Sir Tony Blair, the former British prime minister. Professor of Financial Law and Ethics at the Centre for Commercial Law Studies, Queen Mary University of London, he served as a High Court Judge in England and Wales for nearly ten years, and was Judge in Charge of the Commercial Court from 2016.