The arrests in Britain, France and Romania came after a 10-month investigation into a network of smugglers who were largely operating out of northern France, a police statement said.
Police were tipped off in August 2018 following a string of arrests of Romanian lorry drivers who were trying to cross the Channel “with migrants hidden inside their vehicles”, police said.
“Operating within the scope of Romanian transport companies, with the participation of their managers… (the drivers) took the prospective immigrants from ports” in northern France, Belgium and The Netherlands to the UK.
The investigation was carried out in coordination with European police network Europol and supported by EU judicial agency Eurojust.
The migrants could be hidden in a lorry's trailer, in the driver's cab or even under the wind deflector on the top of the cab, investigators said.
“The migrants, sometimes more than a dozen at a time, were 'stored' there for several hours or even several days” before being loaded onto a boat destined for the northern English port city of Hull, police said.
A first arrest was carried out on June 10 in the French port of Dunkerque of a trucker “trying to smuggle two migrants” across the channel.
During the raids, police arrested the ringleader and nine of his accomplices in Romania, along with six other people in Britain and France.
Investigators found evidence of at least 259 attempts to smuggle migrants across the Channel, 167 of them successful. The network managed to sneak at least 327 people onto British territory, with 140 of them stopped at the border.
The smuggling ring racked up profits of nearly 3.6 million euros ($4.1 million), police said.
Those arrested in Britain and Romania will be handed over to the French authorities.