Security was tightened around the ferry port and the entrance of Eurotunnel last year after a spate of nightly incidents that saw hundreds of people at a time attempt to enter both facilities, often disrupting tourist traffic.

A few dozen migrants were estimated to succeed in making it to Britain each night at the peak of the incidents.

Efforts to enter the ferry and tunnel terminals tailed off with the introduction of new security measures, including a “moat” of flooded, low-lying land around the tunnel entrance.

Consequently, migrants are now forced to travel further from Calais to stow away in lorries heading for the tunnel or cross-Channel ferries.

“Each lorry is packed with dozens of migrants and many are stopped before they reach England,” a regional security official said.

“But we are certain that a few get through. The estimate is around 200 a week. We know others are crossing in small boats or vans,” the official added.

The Home Office keeps no official tally of the number of illegal migrants entering Britain as it is difficult to estimate the numbers who pass through without being caught, but an official suggested that the figure might be “exaggerated”.

However, unprecedented numbers of migrants are flooding into the notorious “Jungle” camp in Calais, indicating that that they know their chances of crossing the Channel are good.