This report was prepared for the 29th biennial Congress of the International Federation of European Law (FIDE) to be held in The Hague in May 2020. It is the national report for the United Kingdom in response to Topic 3 of the 2020 FIDE Congress, titled ‘EU Competition Law and the Digital Economy’. This report offers an overview of UK competition enforcement in digital economy markets by answering twelve questions organised into four sections. Part A summarises key UK antitrust and merger decisions, agency publications, priorities and goals of enforcement in digital economy markets. Part B focuses upon the definition of markets and conceptualisation of market power by UK authorities in digital economy cases in light of their challenges and particularities. Part C offers a detailed overview of the issues underpinning UK antitrust and merger scrutiny in this field: the types of conduct investigated, relevant factors and concepts, theories of harm, efficiency justifications and remedies in digital economy cases. Finally, Part D identifies the potential for incoherent enforcement in this field from two different sources: the overlap between UK competition law and ex ante regulatory regimes (e.g. consumer protection, data protection); and the overlap between the powers of various UK competition decision-makers (e.g. sectoral regulators, the Competition Appeal Tribunal, and the courts)