Drastic changes have taken place in UK electricity policy over recent years as government has sought to address the challenges associated with energy security, affordability and commitments to reduce carbon emissions. This study investigates the underlying policy changes between the year 2000 and 2012, particularly the Electricity Market Reform, as the most fundamental transformation in the British power market since liberalisation, almost three decades ago. It illustrates that although this policy had revised the long legacy of market-based and technology neutral electricity policymaking, it was yet to be claimed as a wholesale paradigmatic shift, because, as of 2012, it still suffered from a form of paradigm ambivalence and socio-technical lock-in. Furthermore, this research identifies an accumulative process of policy change explaining how a complex set of dynamics transformed the UK electricity policy mix. The thesis relies empirically on conducting 53 semi-structured interviews as well as scrutinising policy documents and relevant secondary studies. The thesis draws relevant approaches within policy studies that attend to address continuity and change in policy frameworks, in particular the Advocacy Coalition Framework (Sabatier 1999) and Policy Paradigm (Hall 1993) perspectives. The study contributes to this literature in three distinctive ways. First, it questions the adequacy of existing frameworks for conceptualising policy change in ‘large-technical’ and ‘techno-centric’ subsystems, such as electricity policy. In return, it introduces technology preference, as a policy component capturing the socio-technical elements of electricity policymaking. Second, to explain why and how such significant changes had been undergone, it forms a bridge between the characteristics of policy change and the extent that existing policies are perceived as irreconcilable policy failures. By this, it, albeit, moves beyond the conventional typology of change drivers in policy literature. Third, this research extends the emerging concept of negotiated agreement and policy compromise as a pathway to evolutionary changes (Sabatier & Weible 2007). Inspired by Institutional Change theory (Mahoney & Thelen 2010), it proposes that compromised policies are often at the risk of policy reversibility and retrenchment, subject to any shift in the contextual conditions they have originated in. Overall, the thesis provides an understanding of one of the very complex and contemporary cases for studying policy change theories.