The Vietnamese nationals - including men, women and children - were discovered on an industrial estate in Grays in October 2019.

They died when they ran out of air in temperatures of up to 38.5C (101F) after desperately trying to raise the alarm.

Marius Mihai Draghici, an alleged ringleader of a people-smuggling gang, was detained by police in Romania last August and charged with 39 counts of manslaughter and conspiracy to assist unlawful immigration.

The 50-year-old pleaded guilty on Friday to the charges at a hearing at the Old Bailey.

In 2021, four other defendants were jailed for their roles in the deaths of the victims.

Two men were convicted in 2020, while lorry driver Maurice Robinson and haulage boss Ronan Hughes admitted manslaughter.

Read more:
The perilous journey that left 39 dead

Prosecution lawyer Bill Emlyn Jones KC said he was "disinclined to accept there was no financial reward" for Draghici's involvement, despite not being able to point to any cash being handed over.

Defence barrister Gillian Jones KC said Draghici would prefer to be sentences "sooner rather than later".

Journeys would cost up to £13,000

The court was told how the operation was long-running, with smugglers standing to make more than £1m in October 2019 alone.

Between May 2018 and October 2019, a total of seven smuggling trips had been identified, with the court hearing there were likely more.

Migrants would get on lorries in a remote area of the continent, to be taken to the UK where a fleet of smaller vehicles - organised by the previously convicted Gheorghe Nica - would take them to a safe location until payment had been made.

The fee was said to be between £10,000 and £13,000 for a "VIP route", in which the driver of the lorry was aware of the presence of the migrants in the trailer attached to the cab.

However, some of the trips were stopped by border staff and residents in Orsett, Essex, who had repeatedly reported people being dropped off - but the journeys did not end until the migrants were found dead in October 2019.