It’s known by people who live there as “the town of heaven” which offers “everything you could possibly want”. Not only is there scenic beauty with mountains, beaches and the sea all around but within the town itself there’s a thriving high street and people move here for the lifestyle as much as the chance to make a living.

But Newport, on the coast of Pembrokeshire, was once at the heart of a drug-smuggling ring that is remarkable even by today’s standards — involving hidden underground chambers, Rolls Royce cars, speedboats, suitcases of cash in off-shore banks and “the man with the rubber face”.

The plot, which sounds more at home in a James Bond film than one of the most rural settings in Britain, started in 1983 when some villagers noticed strangers in the area paying for drinks in the local pubs with £50 notes. It turned into an investigation into a worldwide drug-trafficking operation. Even today, what happened to the shadowy people running that operation is unknown. Had they succeeded, a town that is today known for its scenery and quality of life could have been the epicentre of drug distribution in the UK.

But they never got that far. When locals started to think these strangers flashing cash seemed a bit odd, they decided to look into it, no doubt never imagining where their curiosity would lead.

“There were guys staying in Dinas Cross [a small village near Newport] and spending an awful lot of money,” Sue Warner, who lived on a farm overlooking the coast near Newport with her parents, told the BBC.

“So one night my dad decided to camp on the cliff top with neighbours… then things started to unravel.”

What those neighbours found was also what some local lobster fishermen had started to notice: people on a remote beach only accessible by boat or via a life-threatening climb down the cliff face. When confronted, they claimed they were training for a wildlife expedition to Greenland but they weren’t believed. When police officers carried out a search of the bay, they were with a farmer who happened to pick up a stone and throw it. When that rock made a hollow sound when it hit the ground, they cleared away pebbles and rocks and found a hatch leading to an underground bunker, dug deep under the beach and into the surrounding cliffs and lined with fibreglass resin. Inside was tens of thousands of pounds worth of equipment including outboard motors and large inflatable ribs. Operation Seal Bay was launched.

Police suspicions went first to the IRA and its gun-runners. But a few months earlier a large bale of cannabis resin had washed up on another beach nearby. Not long after that bale had washed up, a man called Robin Boswell had carried two suitcases containing £757,000 in cash into a bank on the Isle of Man. When police in Wales arrested Boswell they found he had 17 aliases and was already under investigation for drug smuggling in the Home Counties.

“He was a mystery man and clearly not up to any good,” Don Evans, who was then a detective chief inspector with Dyfed-Powys Police, told the BBC. “He wasn’t going to tell us anything. But… he was wearing walking boots with specks of fibreglass resin.”

The day after “gentleman smuggler” Boswell’s arrest, a man called Soeren Berg-Arnbak was also arrested after being spotted walking on the coast. It turned out he was one of Europe’s most wanted drug dealers and had been on the run for 11 years. He was considered a master of disguise known as “the man with the rubber face”. Having once lived a millionaire lifestyle with a luxury yacht and villas in Italy and Switzerland, he had turned up in Pembrokeshire having gone on the run.

As police widened their net, Boswell’s former wife, Susan, was also arrested as was a man called Donald Holmes, who had been under surveillance by the Metropolitan Police for suspected cocaine trafficking. As the investigation broadened and detectives in Wales spoke to those in London, they mentioned a man they called “Safari Joe” who had been spotted in rural west Wales wearing a white safari suit and driving a white Rolls Royce.

Detectives in England produced a picture of Holmes and Detective Sergeant John Daniels told the BBC that when he saw the picture he thought: “That’s Safari Joe.” Holmes lived a life of luxury in London with Porsche-driving Susan Boswell. When police examined an expensive leather bag owned by Holmes they found pornographic pictures (including of himself) and a telegram linking him to the Jafaar clan in Lebanon, a heavily-armed and infamous tribe around 5,000-strong which is still active today.

“I would suggest that Holmes’ communication with them is illustrative of the level at which these guys were operating,” Peter Walsh, author of Drug War – The Secret History, told the BBC. “These were the guys you went to if you wanted to buy tonnes [of cannabis].”

They also found £30,000 of cocaine in a bank safety deposit box owned by Holmes. But despite the involvement of these rich, glamorous-appearing international drug smugglers, police in Wales suspected there was someone local helping them out on the ground too. They were right. And eventually they found him: a man living quietly in a caravan in rural Pembrokeshire, who was tracked down and spoken to by the BBC for their Cannabis Cove: Operation Seal Bay documentary, which is available to watch on iPlayer.

Known only as Jim, he turned out to be one of the men seen on the beach by locals: “They woke me up one morning in my caravan and I was surprised,” he recalled. “I don’t know how they got to me. I thought I’d got away with that. I wasn’t used to dealing with police. They piled it on and frightened me.”

Over the course of 36 hours, Jim gave an extraordinary account of his involvement with Boswell and his crew which blew the case open. According to former detective Evans: “It was the best statement I’d seen in the whole of my service.”

Jim had once modified cars for Boswell having met through a mutual acquaintance, but what began as manual work soon spiralled into a plot that stretched from Pembrokeshire to Morocco, Lebanon and beyond. He revealed how they were lucky ro survive smuggling drugs by boat across the Mediterranean in deadly weather, sailing their packages all the way to Wales, their final destination. Jim also helped Boswell move boats and boating equipment to the underground bunker on the beach, which was the place they planned to stash 3.5 tonnes of cannabis having sailed out to a “mother ship” in the Irish Sea to collect it.

Seven people ended up being charged with conspiring to import drugs into the UK after the police investigation. While one of them, Holmes, was in custody in Swansea Prison, a man pretending to be an “American law enforcement agent” gained access to him. He was, in fact, an accomplice who wanted to figure out how they could sell the drugs in order to finance the legal defence of those in custody. Meanwhile, the prosecution went ahead, despite the fact that no drugs had in fact been seized. Police faced a further blow when Susan Bowles, local man Jim and another defendant called Kenneth Dewar pleaded guilty. Due to laws at the time, this meant evidence including Jim’s confession could no longer be used against the other defendants.

But the testimony of the Newport locals swayed the case: “What stands out to me is the quality of the evidence given by the local people – genuine, hard-working, you couldn’t have had better people,” Don Evans told the BBC.

“They never challenged any of that evidence,” said prosecution solicitor Mike Hughes. “Because really they realised how dangerous it was. These people came across as extremely honest with a sense of public duty.”

The prosecution also speared Holmes on the stand, while Berg-Arnbak refused to give evidence. But Boswell took the stand and claimed he was not smuggling drugs into the country but was, in fact, involved in a secret operation to salvage a U-boat containing Nazi gold belonging to Hitler’s deputy, Martin Bormann, which had sunk in the Irish Sea around 15 miles off the Pembrokeshire coast.

Robin Boswell was jailed for 10 years, though none of his considerable assets were seized. After he was released from jail he established an organic vegetable supply company in London. Michael Mansfield, the QC who defended him, signed up to a weekly delivery “for a couple of years”.

Soeren Berg-Arnbak was jailed for eight years; Ken Dewar, who helped build the underground beach chamber, was jailed for five years; and Susan Boswell was jailed for 18 months

But Donald Holmes was cleared of conspiracy and jailed for just 18 months for possessing cocaine. Having been on remand for a year he walked free soon after the court case. Around two years later, he resurfaced in Peru with around 25kg of cocaine on board his boat. He was sentenced to 15 years in prison in Peru. No trace of him has been seen since: “I would be very surprised if he survived that,” one former detective said. If still alive, Holmes would now be in his nineties.

Local man Jim was jailed for six years: “That was quite a serious outcome considering they never found any drugs,” Jim told the BBC. “I can’t say I’d like to do that again. But I don’t say that I regret it either, really. Some of it was very exciting, you know.”

Nothing like the case has been seen since in the UK. In fact, the likes of Boswell were the last of the so-called “gentleman smugglers” as more professional, and more violent, criminals emerged, often running their operations from the costas of Spain.