Retrospective tax legislation imposes or increases a tax charge prior to the legislation being introduced. Although this is a controversial practice, retrospective provisions are often introduced to mitigate the risks to the Exchequer from tax avoidance.

The Chancellor Rishi Sunak presented the 2020 Budget on 11 March. The Finance Bill 2019-21 was published on 17 March, and completed its scrutiny in the House of Commons on 2 July. The Finance Act 2020 received Royal Assent on 22 July.