A2.211 Brexit and the implementation period
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The UK negotiated a Withdrawal Agreement and left the EU on 31 January 2020 (referred to as 'exit day') with an 11-month implementation period up to 31 December 2020.
During this implementation period, the UK was no longer a member of the EU but was subject to EU laws, remaining a member of the single market and customs union. On 24 December 2020, the European Commission and UK Government announced an agreement in principle on the legal terms of the future EU-UK relationship ― the EU-UK Trade and Cooperation Agreement (TCA). The TCA was signed by UK and EU leaders and then approved by the UK Parliament on 30 December 2020, but still had to be ratified by the European Parliament. However, the UK and EU agreed that the TCA would apply provisionally from 1 January 2021. The agreement was subsequently ratified by the European Parliament and entered into force on 1 May 2021. The UK has enacted the EU (Future Relationship) Act 2020, which makes provision to implement the TCA in the UK.
While exit day was important in terms of being the date the UK ceased to be an EU member state, the majority of key domestic tax changes associated with Brexit take effect from the end of the implementation period (specifically, 11pm (GMT) on 31 December 2020, referred to as 'IP completion day'), including the full repeal of the European Communities Act 1972, incorporation of