The following is taken from an email circular released by HMRC:
Whether you are heading to Northern Ireland or the Republic of Ireland from ports in Great Britain, there are new processes you must follow.
Before travelling to the Republic of Ireland
If you’re an HGV driver using a Ro-Ro ferry service to the Republic of Ireland (accompanied or unaccompanied) you need to submit a Pre-Boarding Notification (PBN) to Irish Customs before you leave Great Britain.
You are responsible for ensuring you have the correct documentation at the border and that the PBN is submitted using information provided by the importer. However, the PBN may be created by anyone in the supply chain that has the required information.
Only 1 PBN should be created per vehicle irrespective of the number of consignments in the vehicle.
Vehicles will not be allowed to board ferries heading to Ireland without a valid PBN.
PBNs are created on Irish Revenue’s Customs RoRo Service website.
A PBN user guide is available to help you.
Before travelling to Northern Ireland
You’ll need a Safety and Security (ENS) declaration.
From 00:01am (GMT) on 8 January 2021 all goods crossing from Great Britain to Northern Ireland using a Goods Vehicle Movement Service (GVMS) location (Belfast, Larne, Warrenpoint) will require a Goods Movement Reference (GMR).
To get a GMR you will need to:
You can use the free Trader Support Service to generate and submit ENS safety and security declarations to HMRC. After submitting these, the Trader Support Service will provide you with the information you need to input into GVMS to receive authorisation to move goods.
You can find out more about GVMS in GOV.UK guidance.
Help and support
Register for the Trader Support Service to get information and advice to help you prepare for new processes.