Abstract
Traditional analyses of grass roots involvement in political parties have focussed almost exclusively on formal members. However, recent analyses across a range of democracies have shown that non-members (supporters) are playing important roles within political parties, including election campaigning, candidate and leader selection, online policy deliberations and even policy formation. The growing literature on this topic suggests that the involvement of supporters may be a function of party structure and availability of online recruitment. Using new data collected at the 2015 British general election, this article extends the examination of supporter involvement but challenges these assumptions. It shows that supporter activity is better explained by responses to electoral factors and that the focus on online recruitment seriously underplays the enduring importance of human contact.