A tripartite agreement was signed by Belgium, France and the UK on 15 May 1993, which permitted British officials to carry out pre-embarkation immigration controls for passengers travelling on direct Eurostar train services from Brussels to London and Belgian officials to carry out pre-embarkation immigration controls at London Waterloo International (and subsequently St Pancras International) station for passengers travelling in the other direction.
A tripartite agreement was signed by Belgium, France, and the UK on 15 May 1993, which established a framework for pre-embarkation immigration controls at specific points along Eurostar train routes between Brussels and London.