I’m currently reading THE SPY AND THE TRAITOR by Ben McIntyre (an excellent read so far), about Oleg Gordievsky, a deep-cover KGB double agent MI6 ran for years before he was finally burned (by Soviet CIA mole Aldrich Ames, no less) and had to be exfiltrated from Moscow. Among the info Gordievsky passed on, pretty much on the eve of the 1983 British elections, was that then-Labour leader Michael Foot had been an “agent of influence” for the Soviets. Not a spy or conscious agent but a spreader of disinformation who had been paid by the KGB; a useful idiot, if you will.
MI6 decided to sit on this bombshell in the hope that Thatcher would win, but were prepared to warn the Queen if Labour won the election. They were very, very concerned about the constitutional implications if Labour/Foot won. Of course, as we know, Thatcher did win, and the info was buried (and is being hotly disputed by Foot’s family and Labour following its revelation in McIntyre’s book).
Apologies to Hillary for any comparison with Thatcher, but this is what an alternate history looks like…