Its origins are more coarse. Its a derivative of the cockney rhyming slang Birkley Hunt - I.e. cunt.
2. Archaic - my birk hurts.
3. Cockney - get off me you stupid birkley.
the word however stems from a more sinister background.
a birk originaly was a name for somone that robbs graves, from the last name of a faimed grave robber.
other potential origins are from cockney rhyming slang for cunt.
"we caught these two birks in the graveyard!"
"let me feel your birk!"