Nobody knows where or when this word originated but several plausible explanations date back to Yorkshire and the 1960's including that it is a corruption of the french "oiseau" meaning "bird" as used in the phrase ouiseau head.
My favourite is that it was used on a local football field when a particularly disenchanted supporter shouted that the referee was a "wazzock" it being a portmanteau word made up from "wanker" and "pillock" - but surely that would be a "wannock" "wallcok" (which doesn't work).
Mike Harding (ex-comedian, now radio 2 presenter)says he used the word as early as 1976 in his surreal story, "Beaky Knucklewart",recorded on his "One Man Show" album and also in "When the Martians Landed in Huddersfield" but Harding says he heard it from others probably in Barnsley in the late 1960's. This pre-dates Tony Capstick by 5 years.
You complete and utter wazzock
origin - Northern England
An idiot or daft person
Ahh yer g'ert wazzock
Mild insult, one who is foolish, one who has made an arse of themselves, one who is rather daft.
'person x is a pompous wazzock'
Popularised by Tony Capstick (in "Capstick Comes Home") in 1981 and used since as a minor insult (similar to how "idiot" is used as an insult).
Originally meant "bull's penis" (originally described to me as "bull's prick"). See also "wazz" for another derivative of this sense of the word. Whether it was ever applied to other animals or humans I don't know - but as "wazz" is used for human urination in the West and North of England, I'd imagine so.
Was fairly rare in Yorkshire before Capstick's popularisation of it in 1981.
You great useless spawny-eyed parrot-faced wazzock
(Tony Capstick, 1981)
Idiot used in a fun way - I was told the word in the Mid 1960's by a man from Sheffield who claimed to have been using the word for years
Stop it You stupid Wazzock
can be used to desbribe someone you see as an idiot, or someone obnoxious
That boy is a complete wazzock
Idiot, stupid, making improper public statements
In response to the presidential candidate's comments that the Olympics preparation were "disconcerting", the Daily Telegraph slammed Romney as "devoid of charm, offensive and a wazzock." (July 27, 2012)