The man was arrested on a motorway in Beaconsfield, a town 25 miles west of London
British police arrested a 23-year old man from Northern Ireland yesterday as part of their enquiry into the deaths of 39 Vietnamese people found in the back of a truck near London last month.
"He was arrested on suspicion of conspiracy to traffic people and conspiracy to assist unlawful immigration and remains in custody," Essex Police said in a statement.
The man was arrested on a motorway in Beaconsfield, a town 25 miles west of London, the statement said.
The victims - 31 males and eight women - were found in a truck container on an industrial estate in Grays, Essex, not far from docks on the River Thames, on October 23.
The truck driver, who is also from Northern Ireland, has been charged with 39 counts of manslaughter, conspiracy to traffic people, and money laundering.
A second man has been charged with the same offences and British authorities are trying to extradite him from Dublin.
Police have also been looking for two brothers from Northern Ireland. Police in Vietnam have arrested 10 people there in connection with the deaths.