It's a very murky, embarrassing, and oleaginously classified hole to go down. When you factor in the alleged practice coup at Heathrow it gets very very murky.
Michael Foot was almost definitely an extremely naive soviet cooperator - but not a spy, which is what was alleged (He successfully sued on that particular allegation but a civil case is almost literally meaningless when you take into account that SIS have no declassification policy other than no and MI5 wait decades)
The accounts I have read make it sound pretty harmless - Foot apparently met someone from the Soviet embassy a few times, had discussions about things like the roles of unions in the UK but didn't share anything remotely secret or indeed, and critically in my view, know that the person he was speaking to was KGB. I don't think he was even close to being "recruited".
I seem to remember that one of Gordievsky's own points was that the KGB at that point tended to greatly overstate how important their contacts were to make them look better to Moscow.
> met someone from the Soviet embassy a few times ... but didn't ... know that the person he was speaking to was KGB
Come on.... just a friendly chat about union politics with a man from the communist superpower?
Was there anyone at the Soviet embassy at the time who was not likely working for the KGB to some extent?
Embassies are still to this date I believe a key way intelligence agencies get people into a country. Assume anyone you meet and everything you do in an embassy of an adversary you're in a cold war against are going to be working against you.
Many people believe that MI5 had serious worries that Harold Wilson was a soviet spy.