Forty years ago “the man with the rubber face” was caught in rural west Wales after misjudging the power of local curiosity.

Operation Seal Bay in 1983 broke up an international drug smuggling ring after discovering a secret bunker.

The ringleaders were Robin Boswell, and a Danish actor, Soeren Berg-Arnbak. The Dane had been on the run for 11 years.

Known as a master of disguise, Berg-Arnbak was one of Europe’s most wanted drug dealers.

His arrest followed reports from farmers and fishermen of unusual activity at the bay.

In 1983, the 35-year-old lived a millionaire lifestyle on a luxury yacht, and owned villas in Italy and Switzerland. But on the run, he relocated to Pembrokeshire.

Don Evans was a detective chief inspector with Dyfed-Powys Police, and jointly led the incident room for Operation Seal Bay – the code name given to the investigation – with Det Supt Derek Davies.

Speaking 40 years later, Mr Evans said the the gang’s downfall came from the inquisitive nature of the people of the Pembrokeshire coastal town of Newport.

“These villains totally underestimated the local people and how observant they were,” he said. “In all we took 540 statements from people living in the area.”

Sue Warner and her parents, who lived on a farm overlooking the coast near Newport, informed police of suspicious activity close to the bay, as the gang first drew attention to themselves by spending large amounts of money in a local pub.

“There were guys staying in Dinas Cross and spending an awful lot of money,” she said.

“Paying for drinks with £50 notes and lots of partying going on. Lots of money and nice big cars – people just started to put things together.

“So, one night my dad decided to camp on the cliff top with neighbours. They found two men sleeping close to the site of where the gang were planning on keeping the drugs and then things started to unravel.”

Lobster fishermen also spotted activity at the bay, and informed the Newport inshore rescue crew, fearing the people on the beach might be poachers.

The drug gang members told the boat crew they were training for an expedition to Greenland to film whales and seals. But when the crew did not believe them, they returned with Dyfed-Powys Police officers.

The police carried out a search of the bay with a farmer, who picked up a stone and threw it into the cave. It hit the ground and made a hollow sound.

Officers cleared the ground of pebbles and rocks, and discovered a hatch leading to an underground bunker.

Don Evans could not believe what they had found.

“It had obviously taken a long time to build. It was held up with timber and totally lined with fibre glass resin,” he said.

“It would have taken ages to dig out the sand and rock and build and they would have brought all the materials in by boat.”

Police uncovered £80,000 worth of equipment, including powerful outboard motorboat engines, large inflatable ribs, and building equipment.

At first officers thought it could have been linked to the IRA and gun running, but months earlier a large bale of cannabis resin had washed up on the beach in Newport.

Therefore, police believed it must be linked to the bunker.

The Operation Seal Bay team believed the waterproof bunker would be able to store about £7m-worth of drugs.

Working alongside Berg-Arnbak was Robin Boswell, from London, who was described as the mastermind of the drugs ring.

Police caught Boswell after a stranger matching his description was spotted by two young boys and their mother.

“Robin Boswell was arrested: a man who gave us 17 false names and addresses, he was a mystery man and clearly not up to any good,” said retired detective Mr Evans.

“It transpired after arresting Boswell, that he wasn’t going to tell us anything. But what was unique, he was wearing walking boots with specs of fibre glass resin.

“We thought that’s what we needed to link him to the bunker at the cave.”

Berg-Arnbak was also arrested the next day after being spotted by police officers on patrol near Fishguard.

When he spotted the police, he ditched his rucksack and fled across fields. He then jumped over a hedge and barbed wire fence, without realising there was a 70ft (21m) drop into a quarry on the other side.

He only survived by grabbing a protruding tree root to break his fall and was arrested at the bottom of the old quarry. This ended his 11 years on the run.

Police seized his rucksack, containing a high-powered radio which was being used as part of the huge drug smuggling operation.

On a hunch, officers then set up the radio on a cliff top that night. After hours of waiting, they finally heard a communication.

“The radio equipment came to life and the words ‘Mother, mother. I want to come in to get the dirt off my hands’ were heard,” said Mr Evans.

“That communication was enough. We knew there was a vessel out in the bay wanting to come in to get rid of the drugs that were on board.”

Police officers said they never thought Operation Seal Bay would stretch so far.

“It was a global operation. From the findings on the beach, it became a tapestry that spread from Newport, across London, across France, Spain, and Scandinavia,” said former Det Sgt John Daniels.

“It was clear we had netted the major drugs trafficking team operating at that time.

“We didn’t get to the yacht but it’s like the classic case of solving a murder without a body. To prove something when you haven’t got the physical evidence.

“It was a coup for the smallest police force in the country to take on the biggest drugs gang at the time.”

The Operation Seal Bay team followed the money Boswell had been banking all the way to the Isle of Man.

“In December 1982, Boswell carried two suitcases into a bank on the Isle of Man and banked £757,000, all in notes,” recalled Mr Evans.

“We asked the bank manager why didn’t he think of reporting it to the authorities? His face reddened and he said, ‘Mr Evans it’s not unusual for people to come in carrying a shopping bag with £50,000 in cash.’”

Police also seized cars worth £100,000 in 1983 including a Ferrari, a Range Rover, and a Rolls-Royce.

Berg-Arnbak was sentenced to eight years and Boswell to 10 years in prison. Six other members of the gang were also jailed.

The trial judge commended the police and the people of Newport for bringing the gang to justice.

And keeping a keen eye out for unusual goings on was praised by the prosecution, who said: “These greedy schemes were brought to light because of the neighbourliness or nosiness of local people, the interest and curiosity shown by decent people.”