I understand it comes from the medieval oath 'God blind me'(if I'm not telling the truth). There are others.....'Strewth' is from 'God's truth'. The interesting thing to me isn't that these expressions changed over time, but that they are confined to the capital. One would've thought that the countryside would've been where archaic language lingered longest, but not so. You'd never have heard anyone outside of London saying 'corblimey', & these days not so many in it, before radio/tv.Maybe the Puritan PC boys didn't dare take their anti-profanity campaign into the depths of the Great Wen, for fear of starting a riot they couldn't control.
