On the consequences of UK’s withdrawal from the European Union, you can find detailed information provided by the European Commission on travelling between the EU and the United Kingdom from 1 January 2021 on here.
Please check current Covid-19 travel restriction.
Do I need a visa to enter the United Kingdom?
Travelling to the United Kingdom from 1 January 2021: EU citizens can continue to travel to the United Kingdom without a visa for a stay of up to 6 months. Until 1 October 2021, a passport or identity card will be required for EU citizens to enter the country. From 1 October 2021, a passport will be required in all cases for EU citizens to enter the United Kingdom.