The Finance Act 2021 repeals the provisions in the Finance Act 2019 and the Finance Act 2020 related to the introduction of a carbon emissions tax. These provisions had been introduced to allow a transition out of the EU Emissions Trading System. Another option was on the table, namely the adoption of a standalone UK emissions trading system (ETS). As the UK Government announced its plan to introduce a UK ETS in December 2020, this necessarily implied the repeal of the provisions on the carbon emissions tax. Despite the differences between a carbon emissions tax and ETS, the two options considered by the UK Government were reasonable. More than the form of the instrument (a tax or a trading system), it is its substance that really matters and whether the UK ETS will allow the UK to achieve its objectives in terms of climate change effectively.