Forty-eight Albanian stowaways have been discovered trying to smuggle themselves into Britain in a refrigerated lorry.
They were found and stopped at the Channel Tunnel terminal in northern France.
Using refrigerated lorries and sealed tankers to smuggle people across borders could result in fatalities, according to one Border Force official.
A routine check at the Channel Tunnel terminal in Coquelles at around 9pm on Tuesday resulted in the stowaways being found hidden in the back of the HGV as it waited to board a shuttle to Folkestone, Kent.
The lorry, whose refrigeration unit was not turned on, was empty apart from the Albanian nationals on board. It was due to drive to Dover to pick up a load for delivery to France.
There was no external lock or seal on the lorry when it was checked by Border Force officers who found the 41 male and seven female stowaways apparently in good health.
Three of them were believed to be minors. All were handed over to the French authorities while the Romanian lorry driver was arrested by French border police who are investigating.
Dave Hutchinson, Border Force deputy director for South East and Europe, said: "The dangers of using refrigerated lorries and sealed tankers in this way are self-evident. The consequences are potentially fatal.
"This case demonstrates the complete lack of regard the organised criminals involved in people smuggling have for the individuals concerned. It is even more alarming given that some of those found were minors."
Sniffer dogs, heartbeat detectors, carbon dioxide probes and physical searches are some of the methods used by Border Force officers to find people hiding in vehicles.