Twenty-one people, including children as young as 12, have been found inside a refrigerated lorry entering the UK.
The group, thought to be from Vietnam, were concealed among a load of sparkling water at the port of Newhaven in Sussex on Thursday.
Details of the Border Force operation have only just emerged, but a criminal investigation is under way.
A Romanian man, believed to be the driver, has been charged with assisting unlawful entry into the UK.
The lorry was stopped on its arrival from Dieppe in France, when it was found to be carrying 15 children and six adults, all of whom said they were from Vietnam.
The children did not require medical treatment and have been transferred to the care of social services.
An 18-year-old man and a woman aged 27 found on the lorry have been removed from the UK.
Four other adults are in immigration detention centres while their cases are assessed.
Andrut Duma appeared before magistrates on Saturday accused of immigration offences and has been remanded in custody.