Abstract
Opposition politics in the British House of Commons is dominated by the ‘Official’ Opposition. However, other parties also carry out opposition roles in the chamber. This is particularly true of the third largest party, which is afforded some parliamentary privileges yet is overlooked in studies of Parliament. This article fills this gap, using a case study of the Scottish National Party (SNP) to analyse the challenges facing the third party in the Commons. It additionally contributes to the literature on regional nationalist parties, exploring the micro level variables affecting their agenda-setting capacities within a state level parliament. Drawing primarily on elite interviews with SNP MPs and staff, it finds that third party rights are not as significant as they may appear. Party size alone is not sufficient to guarantee impact in the Commons. Strategies to overcome the inherent procedural constraints of the chamber are also required. In the SNP’s case this included incremental organisational change, a highly collegiate intra-party culture and mentoring from existing MPs during the 2015 Parliament.