A haul of cocaine with a street value of up to £300m has been found hidden inside a luxury yacht in Southampton, the UK Border Agency has said.
Officials found 1.2 tonnes of cocaine hidden in a secret compartment in the £1m yacht two months ago.
The 90% pure drugs were so well hidden in the 65ft pleasure cruiser, the Louise, it took six days to find them.
The border agency said it was the biggest ever Class A drug seizure it had dealt with.
The agency said the drugs inside the Louise originated in South America and were en route to the Netherlands. Dutch police have arrested six men.
They are thought to be an organised crime gang.
French authorities were alerted to the Louise while it was in the Caribbean in May and it was then tracked to Southampton.
Officials spent six days searching the vessel and found the drugs packed in a specially-designed compartment beneath the boat's bathing platform, UKBA said.
It is understood the cocaine was packed inside the boat while it was in Venezuela.
The average purity of cocaine seized at the UK border is 63%, officials said.
Boat owner arrested
The haul is estimated to be worth about £50m wholesale and up to £300m on the streets.
Since the drugs were found in June, the UKBA has helped Dutch police track members of the gang and six Dutch nationals were arrested during early morning raids on Tuesday.
A 60-year-old, who owns the boat, was arrested in Meppel. His three sons, aged 27, 32 and 34, are also being held following police raids in Waalwijk and Heusden.
Two 44-year-old men were also arrested in Amsterdam.
A total of 100,000 euros (£87,300), two Harley Davidson motorcycles, two firearms, a silencer and a quantity of ecstasy were also seized.
Brodie Clark, head of the UKBA's border force, said: "This has been an enormous seizure of cocaine. This is the largest we have on record."
'Ingenious' hiding spot
Asked about how the drugs were hidden, he added: "It was ingenious, it was difficult to find.
"Skilful people spent a number of days looking for it."
David Armond, from the Serious Organised Crime Agency (SOCA), described the seizure as a "great success in the international effort to damage and disrupt the cocaine trade".
He said the high purity of the cocaine meant it would have made about eight tonnes of saleable drugs once cut, the equivalent of seven million street deals.
He said that was "equal to about one third of the requirement for the UK market over the course of a year".
Gert Rip, public prosecutor for the National Prosecutor's Office in the Netherlands, said: "About 40% of all cocaine brought into Europe is trafficked using smuggling routes from the Caribbean.
"Venezuela is often used as a supply line of cocaine for the European market."
In 1994 customs staff seized a 1.245 tonnes haul of cocaine which was found on board the MV Jurata in Birkenhead, however the Home Office said since the bitumen barrels the cocaine was hidden in were also included in the total weight of the haul, the latest discovery is considered larger.