The UK Department for Transport (DfT) has signed and published:
For road – ADR Multilateral Agreement M330. Under ADR Section 1.5.1. Driver training certificates in accordance with 184.108.40.206.2 of ADR and safety adviser certificates in accordance with 220.127.116.11 of ADR.
UNECE Multilateral Agreements are available at: https://www.unece.org/trans/danger/multi/multi.html
For more information on the Department for Transport: https://www.gov.uk/government/organisations/department-for-transport