This term, now widespread in English-speaking countries, spread from the USA in the 1960s. A puzzling misnomer to many, to blow in this context is probably a euphemism for ejaculate, a usage occasionally recorded in the 1950s. This may itself be influenced by the there she blows of whaling cliche. This term probably caught on in Britain and Australia simply because there was no well-known alternative in existence. She gave me a blow job but doesn't like to swallow.
Usage is recent and generally inner urban.