In recent years, a number of European countries have undergone important processes of territorial reconfiguration in the administration and delivery of social services. This has produced substantial divergences in the levels and types of welfare development across regions belonging to the same country. As a result, it has become increasingly difficult to talk about 'national welfare systems' or 'national social models' – although most of the mainstream welfare literature continues to do so. The aim of this study is to explore the political factors that explain cross-regional variation in the development of health care and social assistance policies in three countries that have witnessed the gradual strengthening of regions as arenas of social policy making: Italy, Spain and Great Britain. The research focus is on the effects of two political cleavages, centre-periphery and left-right, on sub-national social policy. The findings of the quantitative and qualitative analyses presented throughout this research suggest that the main driving force in the construction of sub-state welfare systems is the political mobilisation of territorial identities through the creation and electoral consolidation of regionalist parties. Indeed, such parties may use regional social policy to reinforce the sense of distinctiveness and territorial solidarity that exists in the communities they represent, thus further strengthening and legitimising their political role. Additionally, the centre-periphery cleavage may also affect relations across different organisational levels of 'statewide' parties and further increase the relevance of territoriality in welfare politics at the regional level. On the other hand, traditional left-right politics does not seem to play the central role that welfare theories focusing on 'nation-states' might lead us to expect. For left-wing parties, the regionalisation of social governance may present either an opportunity or a challenge depending on the role they play in national politics and on the characteristics of sub-national electoral competitors. Generally, mainstream centre-left parties are torn by the dilemma of maintaining uniformity and cohesion in social protection across the national territory and addressing the demands for more extensive and distinctive social services coming from specific regional communities.