Officers working at Dunkirk on 14 July used a carbon dioxide probe to detect the men who were hiding in steel wire aboard a Slovakian-registered freight lorry.
The stowaways were all handed over to French Border Police and the vehicle was allowed to continue to the UK.
However, the Bulgarian driver and the haulage company now face a potential fine if they are unable to prove they took steps to secure the vehicle.
Heartbeat detectors and sniffer dogs
Carole Upshall, the UK Border Agency’s director for European operations, said, ‘This is exactly why we base so many of our staff in France and Belgium - to stop illegal immigrants before they can reach the UK.
‘As well as using carbon dioxide probes, our staff also have heartbeat detectors and sniffer dogs to detect the presence of people hiding in lorries.’
In 2009 more than 29,000 illegal attempts to cross the Channel illegally were prevented.