Regardless of whether the UK and EU agree a new trading relationship by the end of the Brexit transition period, Northern Ireland’s position has already been set out under the Northern Ireland Protocol to the Withdrawal Agreement (although the UK Government has recently announced it may depart from the terms of the Protocol in a very limited way). This will apply from 1 January 2021.
Under the Protocol, Northern Ireland will have the most complex VAT and customs regime in Europe. Businesses in, or trading with, Northern Ireland should start preparing now to meet the new rules.
The VAT and customs implications of the Protocol are covered in this factsheet.