This PhD thesis deals with the subsidy control regime established by the Chapter 3, Title XI of the EU-UK Trade and Cooperation Agreement (TCA). Since 1 January 2021, the UK has fully left the EU regulatory system. The consequence of Brexit is that EU state aid rules no longer apply in the UK in terms of funding and other forms of support measures granted to businesses by public authorities. The only exceptions to this are set in the Ireland/Northern Ireland Protocol. The TCA, entered into force on the 1st of May 2021, whereby, the EU and the UK have agreed upon rules designed to ensure a level playing field for open and fair competition and sustainable development. In particular, the TCA has the most extensive set of provisions on subsidies seen in any free trade agreement to date. The purpose of this thesis is to analyze the TCA rules on subsidies, discussing in a comparative perspective how they work and exploring in interdisciplinary terms whether they are sufficient to maintain a level playing field between the EU and UK after Brexit. To achieve this objective, the thesis examines in detail the TCA mechanisms, comparing them with WTO subsidy law (in particular within the framework of the Subsidies and Countervailing Measures Agreement) and EU state aid law. Moreover, the thesis explains how economic and political dynamics within the EU-UK relationship have influenced the drafting and enforcement of the TCA subsidy control regime. Given that the UK is the first country to leave the EU, and that subsidy control was a true deal-breaker in the EU-UK negotiations, this thesis undertakes cutting-edge research. Thus, it fills a gap in the academic literature and seeks to contribute to explaining what the EU-UK post-Brexit trade deal means in practice.