G4S: What undercover officer saw

Callum Tulley, 21, was so shocked by the chaos and abuse he saw as a detainee custody officer in an immigration removal centre, he decided to become a whistleblower.

Ten present and former staff have been suspended as a result of his allegations.

For part of a BBC Panorama investigation into Brook House, near Gatwick Airport, Tulley went undercover.

G4S say they have commenced an investigation and alerted the police.