Can a passenger sit on another passenger’s lap in a moving car in Northern Ireland?

No. A passenger sitting on another passenger’s lap is not a lawful substitute for an approved seat and restraint in a moving car in Northern Ireland.

For Northern Ireland motorists, the key is to use the NI rule rather than assuming a Great Britain article says exactly the same thing. The lap occupant cannot be properly restrained and can injure both people in a collision. Children in particular must use the required child restraint or belt according to their age and height.

For this exact issue — “Can a passenger sit on another passenger’s lap in a moving car in Northern Ireland?” — the details that usually decide the answer are the passenger’s age, height, seating position, whether a belt is fitted, the type and approval of any child restraint, and whether a narrow statutory exception applies. Northern Ireland makes the driver responsible for children under 14, while passengers aged 14 and over normally carry their own seat-belt responsibility.

If there are not enough safe seats, do not travel overloaded. Arrange another vehicle or make two journeys. Where the facts of a journey or vehicle differ from the ordinary case, check the exact DfI/DVA or nidirect rule before travelling rather than extrapolating from a similar situation.

Before publishing this answer, the key factual point in “Can a passenger sit on another passenger’s lap in a moving car in Northern Ireland?” was checked against current Northern Ireland official guidance. That matters because road rules, licence entitlements and enforcement details can differ from Great Britain and can change over time; the sources attached below are the ones to re-check if the rule is updated.