Punters have been betting on election outcomes for as long as there have been competitive elections. Electoral spread betting is, however, a relatively recent phenomenon. This article explores the development of this practice in early twentieth-century Britain, charting the markets in election ‘Majorities’ in the period between 1910 and 1931. Unlike modern Internet-based spread betting, which has proved remarkably accurate in predicting election outcomes, interwar Majorities market traders were repeatedly wide of the mark. This article makes use of social science theory and historical analysis to explain the predictive failure of these interwar markets. Political punters, it argues, were drawn from a narrow socio-economic and geographic spectrum, and consequently did not have access to the range of information necessary to make informed decisions about politics. Further, the uncertain political environment — characterized by the rise of Labour, the quadrupling of the electorate between 1918 and 1928, and the emergence of genuine three-party politics in the 1920s — created unprecedented difficulties for would-be political punters. In retrospect, Labour's displacement of the Liberals and the hegemony of the interwar Conservative Party may seem inevitable, but at the time the progress of party politics struck both participants and observers as much less certain.