On 23 April 1964, Anthony Blunt confessed to MI5 that he was a Soviet spy. Queen Elizabeth II was informed shortly after. Rather than being tried for treason, Blunt was given full immunity from prosecution, on the proviso that he would feed information about the Soviets to MI5. The public knew nothing of this. Blunt, a prominent art historian, went on to Keeper of the Queen's Pictures.
Blunt's identity was represented under the name 'Maurice' in Andrew Boyle's bestselling book The Climate of Treason, published in laye 1979. With this, Prime Minister Margaret Thatcher went to the House and revealed Blunt's treachery. Blunt was then, finally, stripped of his knighthood.
BBC The World at One: Andrew Boyle discusses the Climate of Reason [click]
Blunt Interview, BBC 9'OClock News, 20 November 1979 [click]