This article examines the impact of the Spanish Civil War on the political left in Britain via a study of the response engendered by the conflict in Aberdeen and Dundee. The Spanish Civil War united the British left in sympathy with the Republican Government yet failed to produce a unified national campaign. The article contends that, rather than being viewed as primarily the result of decisions made at a national level, the failure of a national campaign to emerge must be understood within the context of the diverse nature of grass-roots relationships on the left. These pre-existing local patterns of activism, conditioned by social and economic realities, interacted with international events and national decisions to shape distinctive political responses to the Spanish Civil War. The article considers, in particular, the manner in which local campaigns in support of Republican Spain were shaped by the nature of previous campaigns against the domestic policy of the National Government. As such, it is argued that events in Spain did not create unity on the political left ex nihilo. In those areas where there had been an established tradition of cooperation on the political left Spain served to strengthen such unity; where such a history of shared political activism was absent, Spain alone could not provide it.