This is what reads on the website www.gov.uk in the following link on January 13th, 2021:
"You can only travel internationally – or within the UK – where you first have a legally permitted reason to leave home. In addition, you should consider the public health advice in the country you are visiting.
If you do need to travel overseas (and are legally permitted to do so, for example, because it is for work), even if you are returning to a place you’ve visited before, you should look at the rules in place at your destination and the Foreign, Commonwealth and Development Office (FCDO) travel advice ( https://www.gov.uk/foreign-travel-advice ).
UK residents currently abroad do not need to return home immediately. However, you should check with your airline or travel operator on arrangements for returning.
Foreign nationals are subject to the ‘Stay at Home’ regulations. You should not travel abroad unless it is permitted. This means you must not go on holiday.
If you are visiting the UK, you may return home. You should check whether there are any restrictions in place at your destination."