If it had been a success, the audacious raid on ‘priceless’ diamonds on public display would have been one of the biggest hauls in British criminal history.

Planned and plotted on a rural Kent farm, the idea was brazen. Burst into the Millennium Dome in Greenwich - just months after it had opened in 2000 - break into a secure ‘fortress’ guarding some of the world’s most valuable gems, and then escape, James Bond-style, down the Thames in a speedboat.

Then, for the crooks involved, kick back and enjoy a life of luxury in foreign climes.

The reality, however, proved to be rather different.

Little wonder, then, it has inspired the Guy Ritchie-produced three-part Netflix docu-drama The Diamond Heist, which airs this week. Because this is one of those stories where fact is stranger than fiction.

And the best-laid plans of the criminals would all start unravelling in the most inauspicious manner - outside a pretty countryside pub in Kent in the early hours of August 17, 2000.

Terry Millman, the driver of a white Ford Transit van, had reversed into a fence outside the Halfway House pub on the Horsmonden Road in Brenchley. And promptly fallen asleep.

Officers had received a call at 1.35am to attend.

Upon arrival, Millman was breathalysed and returned a reading comfortably over the legal limit. He was taken down to Tonbridge police station, where checks also revealed the van had false plates and had been stolen.

In isolation, nothing to create headlines.

But Millman had already been spotted as part of a police surveillance operation. And his decision to have one too many drinks that night whilst behind the wheel of the van would be key to police getting - and staying - one step ahead of a daring crime involving a jewel described as ‘priceless’ and insured, at the time, for £100 million.

The Millennium Star was truly a gem of rare beauty. Owned by specialists De Beers, it is described as the “world’s largest top-colour internally and externally flawless pear-shaped diamond”.

And, in 2000, it, along with a host of other valuable gems, was the star of the Money Zone at the Millennium Dome - one of various themed areas in the building built to stage an exhibition to mark the dawn of the 21st century. Collectively, they were called the Millennium Jewels.

Today, the building is better known as the all-singing, all-dancing entertainment venue The O2 Arena.

As midnight chimed and 1999 morphed into 2000, laser beams lit the diamond before an audience which included Queen Elizabeth II, the Duke of Edinburgh and then-Prime Minister Tony Blair. But its dazzling beauty had also captured the attention of crooks.

Crooks who had already seen two high-profile attempts at stealing booty worth millions of pounds foiled that same year. Before the year was out, they would drive a JCB into the Dome, armed and tossing smoke grenades as they went, in an attempt to swipe the diamonds. They felt confident they could evade capture, be in and out and escape by speedboat down the Thames. They were hopelessly deluded.

And Millman was the unwitting key to tracking the gang down. Crucially, he had form - having previously served time for armed robbery. As he was checked in, alarm bells among the officers started to ring.

As he left the station, released on bail, officers from the Met Police’s special operations unit - SO11 - followed at a discreet distance. They knew if they remained patient, he could lead them to the others involved. They were, from the outset, convinced this gang were behind the previous efforts and was planning another bid to score big.

Kent Police and the Met’s Flying Squad - the dedicated team tasked with tackling the biggest robberies in London and who had spearheaded the investigation into the Brink’s-Mat robbery in 1983 where £26 million of gold bullion was stolen - had joined forces after an aborted, violent raid near Aylesford in July.

In dramatic scenes on an industrial estate in Forstal, crooks had tried to hold up and forcibly break into a Securicor lorry containing some £9 million in cash due for distribution to local banks.

The gang rammed the reinforced truck with a lorry fitted with a giant spike, threatened to blow it up (by planting fake bombs on the cab - they were, in fact, Fray Bentos Steak and Kidney Pie containers obscured by a coating of paint and adorned with flashing lights) and fired warning shots at bystanders before police arrived and they fled empty-handed. Pursued, they were spotted clambering into a speed boat and escaping down the River Medway - but not before firing again, this time at police. No one was injured.

It bore remarkable similarities to another botched raid in Nine Elms - close to Battersea Power Station in the February of 2000 - which the Flying Squad were probing but struggling to get a lead. A van with a spike was used then too in an effort to break into a van containing £10 million.

Now-retired Kent Police Detective Sergeant Ian Dampier, who was part of the team at the time, explains: “Millman was an armed robber. The vehicle he was in was stolen and had the same forged tax discs as the ones used in the Aylesford robbery. That was a crucial moment. There was a lot of activity after that because we’d found a main player in this gang.

“He was a character. He was an old-style criminal, incredibly loyal and probably a bit of a liability.”

By mere coincidence, an eagle-eyed Kent Police officer had spotted some suspicious behaviour at Tong Farm in Brenchley in the April of 2000. Stolen cars had been seen and, by chance, among them were vans used in the Aylesford raid. As well as Millman’s Ford Transit. His drunken early hours prang allowed police to put a name to him.

Working with the Flying Squad, the farm was put under heavy, around-the-clock, surveillance. It was owned by the Wenhams, a family of scrap metal dealers. “They mixed with some quite highfalutin people,” explains the former Kent detective, “and they would have seemed like lovable rogues.”

Lee Wenham, 32 at the time, was beginning to pique their interest.

A few days after Millman was arrested, his fingerprints matched those found in the abandoned vehicles used by the masked gunmen behind the botched Aylesford raid.

As they continued to pay close attention to the farm, they discovered that Lee Wenham had made one trip to the Millennium Dome and planned another in the coming days - which given the dire publicity surrounding the Dome and poor ticket sales for the exhibition - prompted little more than a snigger among investigating officers when first mentioned.

It was only when one of the Met officers pointed out the diamonds on show there, that they considered it a possible target. Not to mention its position on the river providing any would-be thieves with an easy escape route.

By the time they discovered the diamonds on display - with the Millennium Star as the centrepiece - were worth, in total, a conservative £350 million, things started to add up.

Operation Magician, as it was coined, was underway.

On August 25, plain-clothed police followed Wenham as he made his way to the Dome. Their working theory was that he was carrying out some reconnaissance visits, feeding back information to the gang.

He was seen entering the exhibit, filming the entrance and the cabinets with a video camera, before carefully making his way to the edge of the Thames and surveying the scene.

Back inside, the diamonds on display were encased in a secure room, with a reinforced case that De Beers estimated would take 30 minutes to drill through with the most sophisticated of available equipment.

As the police investigated further, it became apparent the room was under 24/7 CCTV coverage and, crucially, that the jewels were kept there overnight - rather than placed in a secure safe outside of visiting hours.

The police were now convinced the Dome - and the showpiece diamonds - were the target. On September 1, it emerged the Millennium Star was to be moved to go on display in Japan with a replica put in its place at the Dome. The police were convinced that was the day the thieves would look to strike - intercepting the security van as it travelled from Greenwich to De Beers’ central London headquarters.

More than 300 police - many armed - were deployed along the route, with one police officer even braving high winds and a bitter cold wind by positioning himself in a crane hundreds of metres above the Dome to provide an eagle’s eye view. The diamond itself was left at the Dome in case the thieves got lucky. But it passed without incident, leaving police scratching their heads. Surely, they thought to themselves, they wouldn’t consider entering the Dome itself to steal the jewels?

Yet that same day, when police entered the Dome’s CCTV monitoring room - under the guise of investigating drug dealing on the site - they spotted a man familiar to them on the screens. Ray Betson. A career criminal who had lived in a sprawling luxury home in Kent.

He had first been convicted for burglary at the tender age of 14 and committed a slew of other offences over the years which had seen him spend three years behind bars.

Detectives also believed he had accrued a fortune, running into the millions, through robberies.

He was accompanied by a man also with a shady past - William Cockram - another career crook from South London, whose record included a burglary in Sevenoaks.

Police believed both Cockram and Betson matched descriptions of armed robbers who had stolen £3 million from a security van in Barking in 1996 and a further £5 million from a post office in Hastings after they had convinced one worker they were holding his family hostage.

They were, like Millman before them, casing the joint - inspecting the cabinets which contained the jewels and the security surrounding them.

Tailed by officers, the pair were later seen meeting up with 30-year-old Aldo Ciarrocchi in nearby Rotherhithe. The trio were spotted looking at a brochure of the Dome together and reviewing the video footage they had just taken.

By the end of an eventful, and for the police, enlightening day, the priceless diamond was taken out of the Dome and finally escorted to De Beers.

A replica was left in its place - and the police now knew who the gang involved were.

Surveillance continued on Tong Farm with a JCB - stolen from nearby Tunbridge Wells and fitted with false plates - and a speedboat spotted on the site.

But the Flying Squad wanted to catch them in the act of the heist - going too soon would allow them to press precious few charges other than for possession of stolen vehicles.

So the Met drew up an ambitious plan to catch the crooks in the act - ensuring the support of the Dome’s top brass and even senior government officials in the process. Nothing was being left to chance.

A week after the diamonds were switched, Cockram, Wenham and Betson were spotted leaving Tong Farm towing a speedboat.

Followed, they were spotted preparing to launch the craft just off the Kingsferry Bridge on Sheppey. Unfortunately for them, they had misjudged the tide and were forced to return.

Meanwhile, officers monitoring the farm were perplexed by alterations they could see being made to the JCB.

At the Dome, meanwhile, officers were rolling out their plans. Unaware just when the raid may take place, they drew up a plan of attack with teams on constant standby - while not alerting Dome staff or local police to their activities, desperate to avoid any leaks which may get back to the gang.

On September 12, the speedboat was on the move again - this time towed to Whitstable where the crooks put it through its paces. They weren’t impressed. Two weeks later, Millman bought a new speedboat from a dealer in the town. Using a fake name, he signed the invoice ‘T Diamond’. These crooks had a sense of humour.

Over the coming weeks, the police kept a watching brief, while the criminals added to their ranks. Betson, who was leading the gang, met with Robert Adams - a convicted drug dealer from a notorious London gang. Over a drink in a pub in Maidstone, he was recruited to the team. After the man behind the wheel of the boat dropped out of the gang, a replacement was found in Kevin Meredith, from Brighton - a man with no criminal record but who had borrowed money from Cockram when in debt, and the favour was being called in.

Meanwhile, the modified JCB had been moved to a coal yard in London.

But, as the weeks passed and after several false alarms, police chiefs started to ponder if the whole job had been called off.

Things were then made additionally tense when a Sunday newspaper got wind of the police plan and impending raid. A last-minute deal had to be agreed with the paper to give it exclusive access after the attack on the condition it ran nothing until the gang had struck.

In early November, however, the police finally got word of movement. The speedboat had been moved out of Tong Farm. The tides were right and more than 200 police officers were briefed, again, on their intricate plan. They included a team of heavily armed SO19 officers.

The gang themselves were confident. Months of planning had gone into this - each step of the heist carefully timed. They would, they hoped, be in and out within 20 minutes. Long before the police arrived.

They had no idea officers had been tracking them, knew their modus operandi, knew their names. They were walking into a well-executed trap.

On the morning of November 7, 2000, Betson, Adams, Cockram and Ciarrocchi donned bullet-proof vests, and gloves to disguise fingerprints, and clambered on board the JCB. They wore gas masks to protect against the smoke grenades they intended to use and masks to disguise their faces. Cockram - who with Betson spearheaded the gang - was wearing a jacket in which he intended to stash their multi-million-pound gem haul.

Both the JCB and speedboat had - like the Aylesford job - been rigged with petrol bombs to ensure forensic clues were destroyed after playing their part.

Millman dropped Meredith off at the speedboat and, disguised as a workman, waited on the north bank of the Thames. He would, if all went to plan, drive the gang to freedom and untold riches.

At 8.43am the JCB left the coal yard - under surveillance - while the speedboat was on the move too.

Around 45 minutes later, the JCB rammed through a fence around the Dome and flattened a concrete bollard while picking up speed… it was clear the plan was to ram the Dome itself. And their arrival was certainly not subtle - crashing through its outer wall.

“It sounded like something collapsing,” a member of Dome staff said of the thieves’ sudden arrival. “I just saw a JCB passing me at high speed. I thought it was a crazy person trying to destroy the Dome.”

Aware of what was about to occur, police had diverted most of the early ticket holders away from the diamond exhibition - most of those left were plain-clothed police.

The gang arrived at the entrance to where the jewels were on display - letting off their smoke grenades as they did so.

Using a nail gun - powerful enough to fire nails into steel - and a sledgehammer, they infiltrated the glass case holding the Millennium Star in less than 30 seconds. So much for the 30-minute claim.

But just as they were about to reach in, the police’s carefully planned operation swung into force.

Within seconds the armed team were deployed.

The gang were flabbergasted, frozen in stunned disbelief as swarms of police surrounded them.

Millman was intercepted, while Meredith - who, in his nerves, had managed to be waiting at the wrong pier in the getaway boat - was also apprehended.

For the police, it was a resounding success, a testament to patient surveillance and a belief in their theory. For the crooks, the conclusion of a trilogy of failed, audacious, armed raids.

“There was chaos after that,” recalls ex-Kent Police detective Ian Dampier. “There were all the arrests that then took place, searches and getting the evidence together. It was a joint operation.

“It’s always been seen as the Flying Squad’s job, but we did a massive amount of groundwork. There have been numerous books written about the Dome raid and I haven’t seen Kent Police in any of them. We’d almost been forgotten about.

“One of my colleagues describes this as being a 400-metre relay. We did the first three legs, then the Met ran the last and ran off with all the medals.”

Six more men - including Wenham - were arrested the following morning. During raids of the Wenhams’ farms, Ian Dampier says it became apparent that the sites allowed “for all of the ancillary stuff to take place”.

They found laundry bags, which were believed to be intended to get the money away from Aylesford, reflective coats, shotgun cartridges, tabards, and a Smith and Wesson revolver.

Robert Adams, of no fixed address, and Ciarrocchi, from Bermondsey, were sentenced to 15 years each following a trial at the Old Bailey.

Millman, 57, died of cancer in November 2001, before the trial took place.

Wenham was ordered to serve nine years in prison for conspiring to steal the gems and his part in the Aylesford plot.

Kevin Meredith, the speedboat driver, was jailed for five years after being found guilty of conspiracy to steal.

And Betson and Cockram, who have long been considered the masterminds of the raid, had their 18-year sentences later reduced to 15. However, Betson was jailed again in 2014 for 13 years following a bungled security depot ram raid in Swanley.

“I think money drove him. They’re big rewards, aren’t they?” Ian Dampier explains. “You do get career criminals and for some it’s a way of life, while others stop.

“There wasn’t a love-hate relationship between us and them. It was all in fairly good spirits generally. They were old-style.

“Imagine the planning that goes into this. If it all goes wrong you get nothing but time behind bars.”

Netflix’s The Diamond Heist airs from today.