Since the United Kingdom's withdrawal from The European Union, issued Identification cards are no longer accepted for entry in to the UK.
You will require a passport to enter. Anyone who is planning on coming as part of the official trip from The Netherlands will need to ensure they have one prior to departure.
Lambda Events is not responsible for any refusals at the UK or French border, and if refusal is given by either UK Border Force or French Border Force, Lambda Events is not responsible for your return to The Netherlands