If you are moving goods into or out of the UK and make a customs
declaration, you need an EORI number (Economic Operators Registration
and Identification number). From January 1, 2021, only EORI numbers
starting with GB will be accepted when trading goods between the UK and
non-EU as well as EU countries. A GB EORI number looks like this, for
example: GB123456789000. You can validate your existing EORI number here. If you do not have an EORI number or your number isn't a GB EORI, find more information and apply for it here.