A serving Border Force officer was among a dozen people arrested on suspicion of smuggling guns and drugs into the UK.
The 36-year-old officer, from Dover, was detained by French police near Calais along with three other British citizens last Friday, the National Crime Agency (NCA) said.
They remain in custody.
Authorities seized 11 guns - along with magazines and suppressors - alongside around 34kg of cocaine and 7kg of heroin.
Following the raid, eight men were arrested across Kent by Metropolitan Police detectives, the NCA said.
Six were charged with conspiracy to import firearms and class A drugs, and remanded in custody to appear at Barkingside Magistrates' Court on Monday October 9.
:: Christopher Hendra, 29, of Dunlin Walk, Sittingbourne, Kent;
:: Liam Attwell, 18, of Becketts Close, Ashford, Kent;
:: Terry Willett, 31, of Long Meadow Way, Canterbury, Kent;
:: Daniel Duvall, 36, of Coldharbour Lane, Maidstone, Kent;
:: Craig Brabon, 36, of Hazebrouck Road, Faversham, Kent;
:: Christopher Whitehead, 40, of Orpington, Kent.
The remaining two men were released under investigation.
Dave Hucker, head of the NCA's anti-corruption unit, said: "This operation has brought together law enforcement from both sides of the Channel, and we believe we have prevented the importation of a significant quantity of class A drugs and firearms to the UK.
"Our investigation is ongoing, both in the UK and in France."
The six charged men have been remanded in custody to appear at Woolwich Crown Court on November 6.