Six people, including a British man, have been arrested off the coast of Plymouth after authorities seized 1,500kg of cocaine – worth around £120m.
The National Crime Agency (NCA) said the Briton – from Stockton on Tees, County Durham – and five Nicaraguans were arrested aboard a Jamaican-flagged yacht 80 miles (129km) out to sea.
The men, aged between 24 and 49, were arrested on suspicion of drug trafficking and remain in custody, the NCA said in a statement.
The arrests were the result of a joint operation between the NCA, Australian Federal Police (AFP) and Border Force.
NCA deputy director Matt Horne said: "There's no doubt these drugs would have been sold on into communities across the UK in such ways as County Lines fuelling more crime and misery.
"Organised crime groups (OCG) are motivated by money. The deprivation of these drugs will smash a hole in the OCG's plans and ability to operate.
"Also, the arrests of the men transporting the drugs means the crime group has lost trusted offenders who would have been key to their operation.
More from UK
Emma Raducanu: 10 reasons why the young tennis sensation can claim victory over rival Leylah Fernandez in US Open final
Prince Andrew: Duke of York served with legal papers for sexual assault lawsuit, according to US court document
9/11 anniversary: 'It was like hell was opening up' – how I escaped from the 84th floor of the south tower
"We continue to work with partners at home such as Border Force and those abroad such as the AFP to protect the public from the Class A drugs threat."
Australian Federal Police assistant commissioner Lesa Gale said: "This result should serve as the strongest warning to criminals yet – we will continue to be relentless in our pursuit to target and disrupt your illicit operations and to bring you to justice."