Since their first elections in 1973, the thirty-six metropolitan borough councils in England's six metropolitan counties have been dominated by the Labour Party. In part, this domination reflects the normal exaggerative features of the first-past-the-post electoral system: the largest party in terms of vote share tends to get a diproportionate share of the seats. As well as an exaggeration effect, however, that electoral system is also prone to produce biased outcomes-in that with the same share of the votes cast one party tends to perform much better than the other. This has been the case in the English metropolitan boroughs throughout their existence, with consistent-and often very substantial-pro-Labour biases. As well as indicating the extent of those biases, this paper also decomposes them and shows to what extent Labour's significant electoral advantage there is a function of variations in ward size, turnout, the pattern of voting for the Liberal Democrats, and the efficiency of its own vote distribution relative to that for the Conservatives.