What was a significant constitutional matter that occurred in 2020?

The significant constitutional matter that occurred in 2020 was the UK's departure from the European Union, commonly referred to as Brexit. This event marked a pivotal moment in UK constitutional history, as it involved the country transitioning out of a political and economic union that it had been part of since 1973. The complexities surrounding Brexit included negotiations on trade, citizens' rights, and the future relationship between the UK and the EU.

Brexit had substantial implications for various aspects of governance and law within the UK, leading to discussions about sovereignty, economic policies, and the potential for future devolved powers, particularly in relation to Scotland. It also reignited conversations about Scotland's place within the UK and the possibilities of another independence referendum, as public opinion shifted in response to the effects of leaving the EU.

The other options relate to different time periods or events that do not align with the significant constitutional changes specific to 2020. For instance, the establishment of the Scottish Parliament occurred in 1999, the introduction of a new UK currency has not taken place since the adoption of the pound, and the repeal of the Scotland Act would imply a significant dismantling of devolution which did not happen in that year.