Here is the link to guidance information on this subject available on the GOV website:
From 1 January 2021, if no trade agreement exists between the UK and another country, trade with that country will take place under World Trade Organization (WTO) rules.
Find out which trade agreements the UK has signed by linking on the following link:
Some developing countries are eligible to get trade preferences through the UK Generalised Scheme of Preferences which is available here:
This information is being regularly updated by Government.