A 29-year-old man remains in custody after being found in the luggage hold of a school coach returning from Alpe d'Huez, France on Saturday (5 January).
The coach was supplied by a British firm for St John's school in Marlborough, Wiltshire, and staff and students had passed through French and UK border control on foot before the vehicle boarded the ferry, a spokesperson for the school says.
The man was later discovered when the driver unlocked the hold, St John's says.
He was arrested by one of the parents waiting to pick up pupils who was a special constable.
A spokesman for the Home Office said Wiltshire Police had contacted Immigration Enforcement on Saturday after "one man, who presented himself as Sudanese, was arrested for immigration offences".
The case is being handled by the UK Border Agency.
