The Customs Transit Procedures (EU Exit) Regulations 2018

These Regulations make provision for the international movements of goods, with import duty suspended, under the internationally recognised common transit procedure and TIR Carnet system, with provision for such movements within the United Kingdom. They also provide for such movements of goods under arrangements for NATO forces.

Link: The Customs Transit Procedures (EU Exit) Regulations 2018
Source: Legislation .gov.uk