Can you legally use a mobile phone while supervising a learner driver in Northern Ireland?

No. Using a hand-held mobile phone while supervising a learner driver is prohibited.

nidirect explicitly applies the hand-held phone rule to someone supervising a learner driver or rider, not only to the person holding the steering wheel. The supervising driver must be able to pay attention and assist with safe driving. Put the phone away, set any required directions before moving and arrange to stop safely before making calls or replying to messages.