Customs movements that start ahead of the end of the transition period will continue under the rules in place when the movement started, provided the goods being moved have Union status.

Goods have Union status if they’re in free circulation in the EU, having either originated in the EU or having been imported from outside the EU and released for free circulation.

Goods start their movement when either:

you, or another person on your behalf, collect the goods in order to bring them to:
• Great Britain from the EU or from Northern Ireland
• Northern Ireland from Great Britain

you despatch the goods to:
• Great Britain from the EU or from Northern Ireland
• Northern Ireland from Great Britain

If you’re carrying goods in accompanied baggage, the movement starts when the aircraft, train or vessel on which you are bringing the goods to Great Britain from the EU or from Northern Ireland, or to Northern Ireland from Great Britain, is scheduled to depart.

If you’re moving goods between non-EU countries and the UK at the end of the transition period, from 1 January 2021, the UK will apply a UK-specific tariff to imported goods. This UK Global Tariff will apply for import declarations that are accepted after 11pm on 31 December 2020.

See full guidance available here.