I've found uses of it back to 1985 and at that point it's mostly being used by Conservative chancellors and opinion writers to argue pro-running the country like a business or as a vague metaphor about net flow of money in/out of the country as a profit/loss account. Until the 90s it seems to appear in "scare quotes" in press stories, but gradually just becomes used as a shorthand for "the whole of UK business".