Maurice Robinson, a 25-year-old truck driver charged with manslaughter over the death of 39 Vietnamese migrants in Britain, has pleaded guilty to lesser charges.

Key points: Robinson was charged after the discovery of 39 bodies in a truck container in Essex last month

Robinson was charged after the discovery of 39 bodies in a truck container in Essex last month The 25-year-old was not asked to enter pleas to the other charges against him, including 39 counts of manslaughter

The 25-year-old was not asked to enter pleas to the other charges against him, including 39 counts of manslaughter He will next appear in court in December

The Northern Irish driver admitted plotting to assist illegal immigration and acquiring criminal property when he appeared at London's Old Bailey criminal court on Monday morning (local time).

Robinson has been also charged with 39 counts of manslaughter, conspiracy to traffic people and money laundering but he was not asked to enter a plea for these charges.

Prosecutor William Emlyn Jones told the hearing it was likely to be a large and complex case.

Robinson admitted to having conspired with others between May 1, 2018 and October 24 this year to commit an offence of assisting unlawful immigration as well as acquiring cash which he knew or suspected came from criminal conduct.

No trial date was set and Robinson is next due in court on December 13.

Robinson, from Craigavon, was arrested after police found the bodies of 39 people in the back of a truck he was allegedly driving.

Another 23-year-old man is also due to face court on Monday (local time) in connection with the tragedy, while a third is awaiting extradition from Ireland, accused of involvement in what police believe is a wider people-smuggling syndicate.

The victims were discovered in a truck container at Waterglade Industrial Park in Grays, by the River Thames, in Essex on October 23.

All 39 victims — 36 adults and three minors — were pronounced dead at the scene.

Police initially struggled to identify the victims, 31 men and boys and eight women. Initially, British police believed the victims were Chinese, but later sought help from the Vietnamese community.

Most of the victims were from the provinces of Nghe An and Ha Tinh, in north-central Vietnam.

The oldest of the victims was 44, with the youngest being two 15-year-old boys, and a 17-year-old.

Police in Vietnam arrested eight people in relation to the deaths earlier this month.

The victims are believed to have paid people traffickers for their transit into England.

The discovery of the bodies has shone a spotlight on the illicit human smuggling trade that sees poor people from Asia, the Middle East and Africa make perilous journeys to western Europe, often after paying huge sums to criminal gangs.

Police are seen at the scene where bodies were discovered in a lorry container, in Grays, Essex, Britain October 23, 2019. ( Reuters: Hannah McKay )

ABC/Wires