You are quite right. I read differently elsewhere. Obviously, my sources were mistaken. However, wiki also says, "The opposition Labour Party campaigned in the 1983 general election on a commitment to withdraw from the EEC without a referendum.[14] It was heavily defeated; the Conservative government of Margaret Thatcher was re-elected. The Labour Party subsequently changed its policy.[14]"
I'm not sure what to go with. As it seems to have happened in stages, with different parties steering.
https://en.wikipedia.org/wiki/United_Kingdom_membership_of_the_European_Union#:~: