Originally a running joke in a British TV comedy serial as a means of revisiting the tired old gag of how hilarious extreme stupidity in others can be. The character playing the archetypal InnocentFool? would at a dramatic point whisper to his master - "Fear not my lord, I have a cunning plan". The joke being of course that the plan was neither cunning nor much of a plan. Its delivery was always timed to coincide with the moment of greatest hopelessness and desperation.
The fact that such an unoriginal gag should take root in British society as an almost inescapable catchphrase either says a lot about that particular time (co-inciding with the near-total devastation of the traditional industrial base in parts of Scotland, Wales and the Midlands and North of England which did indeed give an impression of hopelessness and desperation to those of us who lived throuh it) or relates to a more long-lived trait in British humour in the face of shambolic fiascos.
Despite the geographically specific origins, the notion of a plan whose creator's belief in its brilliance and salutory ingenuity is in inverse proportion to its obvious catastrophic stupidity in the eyes of everyone else, seems to me a universal theme. Whether universal or not it characterises many of the gulfs of mutual incomprehension that plague relations between IT technical workers and non-technical "business oriented" managers.