Migrant gangs get drivers to slow down by putting up roadblocks, then force the motorist to carry them across the border crossing.
The trend emerged after a couple from Oxfordshire were the subject of an ambush attempt by 15 thugs on a road outside the port.
Colin McKee was forced to stop when he saw branches placed in the road and was stunned to see a gang emerge wielding 4ft batons.
“About 15 migrants came from behind the branches with batons trailing on the ground menacingly,” he said.
“As they approached I decided to try to get through the roadblock. I drove through the migrants as they smashed batons onto my car and battered the windscreen.
“I realised it was impenetrable and stopped, at which point they swarmed around my car and caravan.”
Mr McKee, 54, had passed the wreckage of another car just seconds before which he thinks had been the subject of an earlier attack.
“One guy signalled ‘shh!’ with his finger and made a slashing gesture, indicating he’d slit my throat if I didn’t comply,” said Mr McKee.
They were eventually rescued when a police patrol car appeared and the gang scattered.
A French police source said: “What happened to these tourists is relatively common now.”
A spokesman for the Pas-de-Calais prefecture, which oversees public order for the region, said tourists are seen as “collateral damage” by migrants.