This thesis explains the forum choices of civil society organisations in Spain and the UK in their legal mobilisation against austerity measures from 2010 to 2020. It also elucidates the theoretical foundations behind these choices. This research identifies the Human Rights Treaty Bodies (HRTBs) and the Special Rapporteur on extreme poverty and human rights as crucial forums for anti-austerity mobilisation. Using Legal Opportunity Structure (LOS) theory, this research emphasises the significance of access, costs, and legal stock in social rights mobilisation. However, LOS theory faces challenges in capturing nuanced actor dynamics, variations in actor engagement with ICESCR, and the involvement of 'unlikely' actors with limited resources in resource-intensive mobilisation strategies. Additionally, it struggles to explain differing forum choices between Spain and the UK despite similar opportunities. To overcome these limitations, this thesis incorporates the mapping of actor dynamics and qualitative interviews. These methods provide a nuanced explanation for divergent actor behaviours, highlighting the pivotal role of actors' perceptions of opportunities in shaping strategic decision-making. This thesis applies LOS and POS theory to the domestic environment, illustrating the significance of understanding the interrelationship between domestic and international opportunities in multi-level mobilisation.
Through the analysis of actor dynamics and qualitative interviews, this thesis challenges the identity theory or the 'logic of appropriateness' in explaining forum choice during crises. Instead, it reveals the emergence of new and unlikely actors in the HRTB system following the Economic Crisis. These organisations were able to mitigate structural barriers to access through network formation and the diffusion of information, resources, and frames. Similarly, this thesis shows that when faced with blocked opportunity at the domestic level, civil society in Spain and the UK adjusted their strategies and targeted institutions deemed most likely to unlock closed domestic opportunities. The Special Rapporteur was perceived as likely to open opportunity through his distinct communication strategy and media attention. Furthermore, civil society were drawn to the HRTBs because of their potential to facilitate access to political actors and provide domestic advocacy tools. In this context, this thesis underscores the significance of actors' perceptions of opportunities and their strategic responses to restricted opportunity in driving forum choice.