I could easily be wrong here (I am FAR too young, so wasn't alive let alone interested in politics then), but didn't the 1975 referendum just require a simple majority (though two thirds voted YES anyway)?
EDIT: I just asked ChatGPT (so it could well still be wrong!):
No, the 1975 EU referendum...
If we're looking at damage done per day in office, then there's only one winner.
However, Truss was such a flash in the pan that history will view her as an irrelevance, or at best as an interesting statistical quirk given how pathetically short her premiership was. A lot of people are...