Great Britain to Northern Ireland: Goods will b subject to new declaration requirements, and may be subject to duties if considered "at risk" of moving to the EU (including Ireland).
Northern Ireland to Great Britain: Moving goods should take place as it does now, with no additional process, paperwork or restrictions - except in extremely limited circumstances to take account of international obligations or duty suspension.
Northern Ireland to and from Ireland: Trade in goods will continue unaffected, with no change at the border, no tariffs and no regulatory checks.
Northern Ireland to and from the Rest of the World: Trading will continue broadly as it does today. Northern Ireland will benefit from future UK Free Trade Agreements and the UK tariff regime will apply to imports.
The changes could see as many as 30 million additional customs declarations a year.