http://thefederalist.com/2018/10/26/how-a-kgb-double-agent-saved-britain-won-the-cold-war-for-the-west/
In his new book The Spy and the Traitor: The Greatest Espionage Story of the Cold War, veteran espionage historian Ben MacIntyre confirms a troubling decision—or lack thereof—that some had suspected for years. This is the fact that in 1983 the man overseeing both British spy services MI6 and MI5, head of British Civil Service Robert Armstrong, knew that Prime Minister Margaret Thatcher’s main opponent in the upcoming election was a KGB agent and did not tell her.
Labor Party leader, member of Parliament, and former employment secretary Michael Foot had been a paid KGB agent for decades, and was still on the KGB books as an agent of influence when he headed the British Labor Party and ran against Thatcher for leadership of England in 1983. Foot would have become prime minister if Labor had won.
MI6 told MI5, its domestic sister agency, and MI5 told Armstrong, but Armstrong kept Foot’s duplicity to himself. Nobody informed Thatcher. According to MacIntyre:
[Armstrong] did not tell Margaret Thatcher or her other top advisers; he did not tell anyone in the Civil Service, the Conservative Party, or the Labour Party. He did not tell the Americans, or any other of Britain’s allies. He did not tell a soul. Having been passed the unexploded bomb, the cabinet secretary put it in his pocket, and kept it there, in the hope that Foot would lose, and the problem would defuse itself. [MI6 operative] Veronica Price was blunt: ‘We buried it.’
With what seems in hindsight a misguided sense of higher duty and a display of undemocratic arrogance, Armstrong put the British Commonwealth in the position of possibly electing a genuine KGB agent as prime minister—a fact its intelligence services knew and did nothing about. MacIntyre confirms this state of affairs from multiple sources. Thankfully, Thatcher and the Tories won in 1983.