This article examines the electoral impact of spillover effects in local campaigns in Britain. For the first time, this is applied to the long as well as the short campaign. Using spatial econometric modelling on constituency data from the 2010 general election, there is clear empirical evidence that, in both campaign periods, the more a party spends on campaigning in constituencies adjacent to constituency i, the more votes it gets in constituency i. Of the three major political parties, the Liberal Democrats obtained the greatest electoral payoff. Future empirical analyses of voting at the constituency scale must, therefore, explicitly take account of spatial heterogeneity in order to correctly gauge the magnitude and significance of factors that affect parties' parliamentary performance.