The usage dates from the 1930s; berk is a shortened version of Berkeley Hunt, the hunt based at Berkeley Castle, in Gloucestershire. In Cockney rhyming slang, hunt is a rhyme for cunt, giving the word its original slang meaning.
berk (plural berks)
- (Britain, slang, pejorative, sometimes affectionate) A fool, prat, twit.
- (Cockney rhyming slang, vulgar) Cunt.
Not perceived as excessively rude, perhaps because its origin in rhyming slang is not well known.
- Belvoir (pronounced Beaver)
- Chambers Dictionary: Entry for berk
- Cassell's Dictionary of Slang. Jonathon Green. Pub. Cassel & Co. →ISBN