Police reveal that the immigrants smuggled into Tilbury port were Sikhs from Afghanistan, as an international investigation gets under way.
Police plan to interview a group of 34 men, women and children who were found in a shipping container at the Port of Tilbury on Saturday.
Belgian police have concluded the immigrants were probably already inside the container when it was dropped at a European port before setting sail for Britain.
International agencies are working alongside British police as they continue their investigation into how the group – including one man who later died – came to arrive at Tilbury.
Police have said the immigrants were Seikhs from Afghanistan. Belgian police have reportedly identified a lorry which delivered the container to Zeebrugge on CCTV footage, but have no information about where it originated from.
Police are hunting the driver of the vehicle as they widen their investigation into the incident.
A spokesman for the federal police in Belgium said it appeared to be “impossible” for the 35 men, women and children to be loaded into the unit in the time it was at Zeebrugge, a port in the north of the country.
He said investigators have been combing CCTV and are “very hopeful” they could track down the driver and company of the vehicle that deposited the container.
The container was one of around 50 on board the P&O Ferries commercial vessel the Norstream when it arrived in Essex.
The immigrants were rescued after port authorities heard banging and screaming from inside the container at around 6.30am on Saturday.
Superintendent Trevor Roe, from Essex Police, said the victims from the Indian sub-continent were now recovering “fairly quickly” and that no one else had been discovered hiding aboard the ferry, the Norstream.
Describing them as victims of “people trafficking”, Mr Roe said they had been in the container a “significant amount of time” and that now police were working with international agencies to establish their movements before arriving in the UK.
Emergency services were called to the port and declared a “major incident” after dock staff heard noises coming from the container.
Mr Roe said that once the door on the container was opened those inside were extracted “very quickly”.
One man died at the scene while 18 were taken to Basildon Hospital with dehydration and hypothermia, two in a serious but not life-threatening condition.
They have responded well to treatment and the 11 adults and seven children are now “medically fit enough” to be released, a hospital spokeswoman said.
Nine people were taken to the Royal London Whitechapel hospital, while a further seven were taken to Southend Hospital, all with the same ailments.
All of those found in the container were conscious when it was opened, apart from the man who later died.
No information has been released about the ages of any of the people or the relationship between them.