The Romanian driver of the lorry has been arrested by the French border police who will investigate.
Dave Hutchinson, Border Force Deputy Director for South East & Europe, said: “The dangers of using refrigerated lorries and sealed tankers in this way are self evident. The consequences are potentially fatal."
In 2000, 58 Chinese immigrants died after being sealed into the back of a lorry which was stopped at Dover.
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New criminal sanctions for those who fail to protect children from sexual exploitation are at the heart of new measures to be introduced.