French fishermen are among a dozen people accused of smuggling more than 200 illegal immigrants across the Channel to the south coast of England.
They are said to have dropped them off at small ports and remote beaches and coves between Plymouth and Weymouth to avoid immigration checks.
Armed officers arrested members of the human trafficking gang in dawn raids in Brittany on Tuesday.
The fishermen and sailing boat skippers are alleged to have ferried more than 200 Albanian immigrants across the sea in their own vessels over an 18-month period. There were 14 trips, mostly in 2012, and the immigrants paid up to £8,000 each, according to French police.
The criminal mastermind behind the trafficking ring, a wealthy Kosovan, was arrested in the port city of St Malo. Another Kosovan, who is thought to have helped to organise the smuggling trips, was arrested at his home in Lamballe, near St Brieuc.
Ten local fishermen and sailing boat captains were also rounded up in fishing ports and towns in Brittany's Cotes-d'Armor region as part of the international police operation.
Last night all the suspects were in custody in Rennes. More arrests are expected in the UK and France in the coming days.
A French police spokesman said: 'This gang are believed to have smuggled around 200 Albanians from Brittany to the southern coast of England.
'It is thought they were dropped off at smaller ports and beaches along the English coast between Weymouth and Plymouth'.
'We are in contact with our counterparts in Britain and inquiries into other gangs possibly involved in people trafficking between Britain and France are ongoing.'
A police source added: 'The method was chosen because it avoids the many checks that lorries go through when they board ferries to the UK.'
The traffickers carried the immigrants from ports in Normandy and Brittany, often travelling in hired pleasure boats. Prosecutor Brigitte Ernoult-Cabot, who coordinated the French operation said: 'There were 14 trips over a period of 18 months.'
Albania is not a member of the EU although it wants to join, so its people, who are among the poorest in Europe, require a visa to visit the UK or work here. If discovered by British officials, Albanians without residency rights face deportation, but many find work in the black economy.
The joint Franco-British operation was prompted by the arrest of two boat captains in January 2013. The skippers, both Bretons in their 20s, had hired a luxury yacht, the Koo 2 Bool, on the pretext of sailing to the Caribbean.
But they were stopped by French customs officers off the coast of Normandy, four miles from Cherbourg, trying to smuggle 15 Albanians to England.
The sailors are understood to have carried out five or six similar trips across the Channel.
The skippers told police they had been recruited by a Kosovan criminal boss.
A French police source said: 'The Kosovan mastermind does not live in France. Police had to wait until he returned until they could launch their operation. He had only been in St Malo for a few days when officers struck.'