When I was young (1950's southern England) I learned that Berkshire, pronounced "BARK-sheer" was a county the other side of London, and that a "berk", pronounced to rhyme with "work" or "jerk", was a deplorable individual. Later I learned that "berk" is rhyming slang for "Berkshire Hunt", thus "c*nt".
But they don't rhyme in my pronunciation! How did this come about? Is it subsequent spelling pull on "berk", did Cockneys at the time say "BERK-sheer", or something else?
EDIT made it clear that I never thought that "berk" and "jerk" were regarded as rhyming slang.