At the end of his life he admitted spying for the USSR for a short time, and accused MI5 man Guy Liddell of also being a spy. His son Thomas has said that his father did not admit to being a communist spy, even when he was dying in hospital in 1979. However, Rees told Andrew Boyle, author of "The Climate of Treason", his reflections on conversations held at All Souls College with Guy Burgess, his great friend. He told Boyle that he had ridiculed Guy Burgess's claim to be a spy. He also told Boyle that Anthony Blunt was the man to follow. Boyle's revelations in the "Daily Mail" led to Margaret Thatcher, the then Prime Minister, announcing to the House of Commons in 1979 that the security services had long known that Blunt was a spy, due to Goronwy Rees's warnings to the security services the weekend that Burgess and Maclean fled to Russia. Nevertheless, Blunt had been knighted.