The European Commission has published a Communication to help businesses, public administrations, stakeholders and citizens prepare for the changes that will take effect on 1 January 2021. As of that date, the United Kingdom will no longer be part of the Single Marktet and the Customs Union.
The document is entitled "Getting ready for change - Communication on readiness at the end of the transition period between the European Union and the United Kingdom".
From the content:
Page 9: Certificates and authorisations of products, establishment requirements, labelling and marking
Page 11: Trade in services