This study shows how interest group-party relations, parties' cross-cutting policy preferences, and competition with challenger parties shape the structure of issue competition on climate policy. It uses the 'most similar' cases of the UK and Ireland to show how differences in party systems influence the structure of issue competition. The study takes up the challenge of integrating salience and position in the conceptualisation of climate policy preferences. Empirically, it provides new evidence on factors influencing climate policy preferences and the party politics of climate change, focusing on interest groups, party ideology, and challenger parties. Further, it identifies similarities between the general literature on interest group influence on party preferences and the literature on interest groups in climate politics, and seeks to make connections between them.