Despite a vast pan-European literature on extreme right parties (ERPs), few studies speak convincingly to questions of party membership and activism. This article draws on a unique membership dataset to examine contextual predictors of membership of the British National Party (BNP), currently the dominant representative of the extreme right in British politics. We operationalize and test for the impact of both demand-side and supply-side factors, including the seldom examined effects of historical legacies, and of party activism and electoral success on membership levels. Aside from congregating in urban areas that are more deprived and have low education levels, we also find evidence of a ‘legacy effect’, whereby membership levels are higher in areas with a historic tradition of extreme right activism. This research is the first ever systematic investigation of national extreme right party membership.