And the vast LSD operation they were targeting included society's respected folk – such as doctors, scientists and graduates operating in the heart of Mid Wales.

The motivation for those behind the operation weren't all financial either. Many insisted they wanted to use drugs to transform human consciousness.

But for all their peace-and-love ideals, their conspiracy was, at the time, the biggest drug ring the UK had ever seen and one of the world's largest.

After officers seized a haul large enough for six million trips, the price of an acid tab on Britain's streets reportedly leapt from £1 to £5 overnight.

The investigation, codenamed Operation Julie, didn't just destroy one cartel.

It arguably represented the final death throes of the 1960s counterculture and turned drugs into the criminal activity it is today, with the associated organised crime and violence.

Many criticised Operation Julie for pushing the drugs trade towards criminal gangs linked to violence

It was 40 years ago this month that police descended on Mid Wales dressed as hippies.

Advertising

In April 1976, 28 undercover drug squad officers from 10 police forces were sent to Devizes in Wiltshire where they were trained to go undercover in Ceredigion and Powys in Wales.

As a result, raids on 87 addresses in Mid Wales, London, Cambridge and France between March and December 1977 would eventually turn up laboratory equipment, more than £1 million in cash and shares and enough LSD for 6.5 million doses.

A total of 120 arrests were made, resulting in 15 convictions and prison sentences totalling 120 years.

Lyn Ebenezer, author of Operation Julie: The World's Greatest LSD Bust, who was working as a freelance journalist in the area at the time, said: "Cardiganshire was at the time the counter-culture capital. The likes of the Rolling Stones, John Lennon and Jimi Hendrix had all made pilgrimages to the area, so perhaps it's no surprise that it became the centre of LSD production.

Advertising

"But we didn't have a clue what was going on with these strange groups who'd moved in.

"To be honest, if anyone seemed more likely to be drug dealers then it was the police acting as hippies, as the actual dealers were all educated professional people who stood their round and blended in really well into the community.

"The dealers and the police would all be drinking in the pub together, getting up to all sorts of daft capers, so when the raids finally came we all had one hell of a shock."

In 2010 Welsh actor Matthew Rhys bought the rights to Mr Ebenezer's book, with the view of making a film.

Howard Marks in 2010

Former drug smuggler-turned-author, the late Howard Marks, who died this week at the age of 70, believed the key to the success of the large-scale drug smuggling ring was its remote location in Mid Wales. Marks, who had inoperable bowel cancer, was not involved in Operation Julie.

But he was aware of the episode, which made headlines worldwide.

When asked about it a few years ago, he said: "The key to its success was its isolation and the discipline of the people involved.

"It used a cellular structure as a model which you find in a lot of organised crime, including terrorism; if one part of the organisation gets busted the others can continue unimpaired."

Marks, who was jailed in the US in 1990 after being convicted of smuggling cannabis, had visited Shropshire recalling his exploits in a bestselling autobiography, Mr Nice, which was later made into a film starring Rhys Ifans,

The two LSD rings broken up by Operation Julie had begun life as one organisation.

Its founders were David Solomon, an author, and Richard Kemp, a chemist, who first successfully synthesized LSD in 1969.

Police were first alerted to the possible existence of the drugs network in 1975, when a Range Rover belonging to Liverpool University chemist Kemp was involved in a fatal crash near Machynlleth.

A search of the vehicle found shreds of a wrapper, which when reconstructed, spelt the words "hydrazine hydrate", a key ingredient in the manufacture of LSD.

Kemp had been recruited in 1969 by Cambridge author David Solomon to manufacture the drug as part of a social experiment to bring world peace through "mind-expansion".

On February 17, 1976, a meeting at Brecon involving a number of chief constables and senior drug squad officers formed a multiforce operation – Operation Julie – Britain's first combined drug busting operation led by Dennis Greenslade.

Surveillance of Kemp noted his regular 50-mile commutes between his home in Tregaron and Plas Llysin, an old mansion owned by an American friend Paul Joseph Arnaboldi, in Carno near Llanidloes. The mansion was put under 24-hour surveillance and listening devices were installed.

On one occasion the undercover officers were left listening to Radio Cymru for an entire day, when sheep gnawed through the bugging devices.

Down the road in Llanddewi Brefi, a group of male officers garnered unwelcome attention when they were suspected of being a "gay cult".

This necessitated the introduction of female officers, including Sgt Julie Taylor, after whom the operation would eventually take its name.

Radical who came to assume a key role

We were idealistic – Leaf Fielding

Operation Julie ushered in a new era of policing that remains the blueprint for cross-force drug operations to this day.

It also arguably represented the final death throes of the 1960s counterculture, shattering the idealism with which many had once viewed the drugs scene and marking the start of a harsher, more brutal era for the narcotics underworld.

In addition, its unprecedented scale and co-operation between forces set the tone for the so-called war on drugs of the 1980s.

One of the radicals who came to assume a key role was Leaf Fielding, an anarchist former public schoolboy who had dropped out of university following his introduction to acid at the age of 18. He began as the tabletter, turning the raw chemicals into individual doses, and later took over the distribution network.

As he recounted in his memoir, To Live Outside the Law, it was the promise of building a new society and seeking a way out of the cold war's nuclear stand-off that drove the gang at first rather than money.

"We were all extremely idealistic," he recalls. "I was convinced that this was the answer to the world's problems. We saw it as a new awakening out of the terrible impasse that the world had got itself into."

In 1973, fearful of police attention, one wing of the co-operative led by David Kemp and Richard Solomon moved to Wales while another branch remained in London.

The influx of these figures into villages and towns like Llanddewi Brefi and Tregaron was less conspicuous than might be imagined. The LSD ringleaders all held down jobs, mixed with their neighbours and stood their rounds in local pubs.

Indeed, like many in the ring, Fielding did not need to take the risks he did. By the time of the raids, he had built up a thriving legitimate business, a health food shop, in Reading. Shortly before the bust he told his co-conspirators he wanted out.

"We began as idealists but then paranoia crept in," he recalls.

After the ring was busted, share certificates and details of Swiss bank accounts provided evidence that the operation had turned into a multi-million pound, multi-national corporation.

Kemp was sentenced to 13 years in prison and his partner Christine Bott, a qualified doctor, to nine years. Their convictions led to the end of the ring's LSD-manufacturing activities.

Fielding, who was sentenced to eight years in prison, observes that the drugs gangs who stepped into the vacuum were far nastier than his own. He said: "Obviously some people did suffer and I don't feel great about that. But some drugs work for some people and others don't."