The article examines the narratives of collective belonging among two migrant groups, Somalis and post-enlargement Poles, who live in the London borough of Ealing (United Kingdom). In order to gain a better understanding of the processes of social identity formation, the article proposes a synthesis of a social identity approach, in particular the recent discursive developments in the field, with a political opportunity structure approach. Drawing upon these bodies of research, the article analyzes the understandings of collective identity among Somalis and post-enlargement Poles according to three sets of social relationships: the group's relationship with the political environment; its relationship with other groups; and its relationship with people who share the same ascribed identity. The findings of the study confirm that social identity is shaped by not only intra- and intergroup cognitive elements but also by the political environment in which a group operates.