When a goods movement from Great Britain to Northern Ireland is deemed ’at risk’ and duties are payable, you are entitled to claim a customs duty waiver from the government covering the cost. This will be a form of de minimis aid. De minimis aid is a small amount of government—provided aid that is unlikely to distort competition rules.
For further information, please refer to GOV.UK and the How to Claim a Customs Duty Waiver Guide.