This article reviews the United Kingdom’s post-Brexit legislative trajectory with an emphasis on windfall tax measures, primarily under the Energy (Oil and Gas) Profits Levy Act 2022, Finance Act 2023 and Finance Act (No. 2) 2023. Drawing a comparative analysis with the European Union’s Regulation on an Emergency Intervention to Address High Energy Prices (2022/1854) and its application in Ireland, the exploration delves into the origins, frameworks and broader implications of these legislative shifts in a post-Brexit environment.