British authorities issued repeated warnings of the increasing threat of people smuggling via Belgium three years ago.
After the discovery of 39 bodies inside a lorry container at Waterglade Industrial Park in Grays, Essex, yesterday, it emerged that Border Force officials highlighted the port city of Zeebrugge as a key embarkation point for "clandestine arrivals" in a 2016 threat assessment.
In the same year, the National Crime Agency (NCA) said the "highest priority" organised immigration crime threat was clandestine activity using roll-on, roll-off lorries and containers.
The NCA said organised crime groups "often use seaports away from the migrant camps”.
It highlighted that improved port controls at Calais and Coquelles in France meant the activity of such groups was "displaced" to other locations on the continent.
Warnings were also made three years ago about smuggling gangs turning to less busy UK ports like Purfleet.
In April 2016, the NCA said criminal networks were suspected to have started targeting quieter ports on the east and south coasts as well as the main Channel crossing between Calais and Dover.
The NCA started running the largest dedicated operation against organised immigration crime in Europe.
At the time, Tom Dowdall, deputy director of the NCA's border policing command, said: "We've seen on the east coast evidence from Tilbury and Purfleet, up as far as Hull and Immingham. And on the south coast from Newhaven to Portsmouth.”
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Richard Burnett, chief executive of the Road Haulage Association, suggested "robust" security checks at Calais and Coquelles were having a knock-on affect in other areas.
He told BBC Breakfast: "That kind of pushes the problem further out to more remote ports, and if we haven't got the infrastructure in place there from a security perspective to check those vehicles then traffickers will definitely use those routes to try and get migrants into the UK.”
An inspection report of Border Force operations in east coast seaports in 2016 warned of the dangers of people being trapped inside lorry containers.
It said: "Groups in unaccompanied, sealed containers are likely to have been placed there by organised people smugglers.
"Since they are unable to release themselves, the risks are high and there have been numerous recorded deaths.”
The report included an example from August 2014 when 35 people, including 12 children, were discovered "screaming and banging" in a locked container being unloaded at Tilbury off a ship from Zeebrugge. Those inside the container had to be treated for severe dehydration and hypothermia, with one man pronounced dead at the scene and four others taken to hospital.
In subsequent years the NCA has repeatedly highlighted the risks of people smuggling from the continent, including from Belgium.
Its serious and organised crime assessment in 2017 said crime groups based in Belgium will have "an increasing impact" after the clearance of the migrant camp in Calais.
In the same report last year, the NCA said: "People smugglers continue to favour hard-sided refrigerated lorries to transport migrants to the UK.
"Belgium has become a location of greater focus for the activities of organised people smugglers in the past year where smugglers of various nationalities operate.
"The number of smugglers located there increased after the closure of the migrant camp at Dunkirk in March 2017.”
Earlier this year the NCA warned there had been an "increasing use of higher risk methods of clandestine entry" which included the use of "refrigerated HGVs”.