We tested how well the Identity-Deprivation-Efficacy-Action-Subjective-wellbeing (IDEAS) model predicts citizens' intentions to engage in collective action opposing their government, and their subjective well-being. Representative samples from Scotland, Wales, and the county of Kent in England were surveyed during the COVID-19 pandemic in October 2020 (N = 1,536). Results largely support our preregistered hypotheses, confirming that the IDEAS model offers a valid explanatory framework for how relative deprivation predicts both collective action opposing one's government and levels of subjective well-being. In the case of collective action, there were significant effects of collective relative deprivation (cognitive and affective) and collective efficacy on social change beliefs, which in turn positively predicted collective action intentions. The role of national identification was more nuanced, revealing both negative indirect effects via collective efficacy and relative deprivation, and a positive indirect effect via political orientation. Findings also suggest interesting directions for future research on national identification.