On 1st Sept 2020, the UK issued instructions for persons placing manufactured goods on the UK market after 1 Jan 2021. These instructions are here.
The instructions detail the situation for the GB market, separate links access instructions for GB companies placing goods on the EU market, and for Northern Ireland. Please follow those links and read the information set out there.
Separate rules apply to chemicals, medicines, vehicles and aerospace. Follow the links for the latest information. Medicines is well elaborated.
There are also rules for goods that are not covered by EU rules. Follow those links for the latest information there.
Finally, some other categories have particular rules, follow those links.
Please read my separate Blog post on UKCA marking. Note, UKCA marking will not be recognised in the EU or Northern Ireland markets. Products currently requiring a CE marking for sale in the EU will continue to need a CE mark.
Note, distributors of EU goods in the UK will become importers from 1 Jan 2021.
Queries should be sent to BEIS.