He joined the Communist Party of Great Britain, but left after reading Isaac Deutscher's biography of Leon Trotsky.
Convinced of Trotskyism, Richardson joined the Socialist Labour League (SLL), and resigned from the faculty at Exeter to become a history teacher at Forest Hill School, South London.
He soon quit the SLL to join the rival International Marxist Group (IMG), and became prominent in the Vietnam Solidarity Campaign.
His funeral at Mortlake Crematorium was attended by 150 friends and former pupils,[7] who draped his coffin in the flag of the Fourth International.
[11] As a keen Egyptologist Richardson was a member of the Egypt Exploration Society, and was fluent in Egyptian hieroglyphics, Geʽez,[2] third century Greek,[12] and French.