["JCMS: Journal of Common Market Studies, EarlyView. ", "\nAbstract\nThis article analyses the European Commission's (Commission) capacity to manage and deepen the EU–UK relationship post the implementation of the Trade and Cooperation Agreement (TCA) and its efforts to expand its competencies within the framework, through the use of the principal–agent theory. Informed by studies on the powers and management roles of the Commission, the analysis focuses on three areas where the institution has demonstrated these capabilities. Our findings show that the Commission used all its available tools to protect the interests of the EU, seize opportunities to deepen EU–UK relations and build an unrivalled pool of policy expertise, whilst seeking to go beyond its role within the TCA. These findings show the Commission retains a broad range of powers and resources, which allows it to manage third‐country relations, whilst also maintaining its influence in the post‐Lisbon European Council framework."]