I remember reading about the mystery of the missing diver many years ago. The link in the previous sentence covers it nicely, but in essence what happened was this:
In 1956, the leaders of the Soviet Union were on a goodwill visit to the UK. There was a bit of a row when Lionel “Buster” Crabb, a Royal Navy diver, “disappeared” in the vicinity of the visitor’s ship. It’s been argued about ever since. Was he on a dodgy espionage mission (well, duh)? Did he have an accident, was he killed by people who didn’t want divers getting too close to their ship? Was he taken away? There were stories that he’d lived for many years afterwards in the Soviet Union, but most people favoured the “killed” theory.
Anyway, now we may have the answer. According to BBC News, Crabb was indeed killed by a Soviet sailor, who has told his story to a Russian documentary. He alleges that Crabb was attempting to fix a mine to the ship. Now I can believe that British security services might well have been up to a lot of not entirely authorised activity in keeping an eye on our visitors, but the suggestion that they would try to blow up Khrushchev’s ship is more of a stretch. But who knows?
 Note: many years after the event, I hasten to add. I’m not that old