It's like something from classic crime fiction. A multi-million pound diamond-encrusted tiara, made for an imperial coronation, was snatched from its stately home display case in the dead of night.

But while the audacious raid by a power tool-wielding gang made headlines in its own right, it turned out to be the beginning of a far darker conspiracy.

It revealed a story of secret filming, smuggled jewels and a group that specialised in shockingly violent burglaries - including the homes of two former England footballers.

The damaged case where the Portland Tiara was once housed now contains only a photograph of the original

The alarms went off at the Portland Collection Gallery on the Welbeck Estate, Nottinghamshire, at 22:00 GMT on 20 November 2018.

Det Insp Gayle Hart, who led the investigation, said: "The security at Welbeck is some of the best I've seen.

"But this was an audacious burglary, more than a year in the planning."

CCTV showed three people who had driven over fields to approach the gallery from the back.

The case lasted for almost two months and included distressing evidence from Ashley Cole

Smashing through a ground floor window, they then cut a crawl hole through a metal security door to access the main gallery.

With a smaller saw - with a depth gauge set to make sure nothing else was damaged - they sliced open an armoured glass display case, seized the tiara and a matching brooch, and fled.

While security had observed the gang on CCTV and called for help, the culprits evaded on-site staff, driving away just moments before police arrived.

From the first alarms sounding, the entire theft had taken less than eight minutes.

The getaway car was found burned out just hours later.

Trophy pieces'

The tiara was made for Winifred, Duchess of Portland, to wear at King Edward VII's coronation

The tiara was commissioned in 1902 by the then Duke of Portland for his wife to wear at the coronation of Queen Alexandra and Edward VII. Made by Cartier, the diamonds were mined in the 1800s.

The gang's trial at Nottingham Crown Court heard it was stolen together with a brooch that had been made from diamonds when the tiara was remodelled. Together, they had a combined value of £3.75m.

"It is difficult to overstate the importance and cultural value of these pieces of jewellery," prosecutor Michael Brady QC said.

"These were trophy pieces of the gallery's exhibition; extremely valuable, unique and of significant historical importance. They were displayed for the public's enjoyment.

"Their theft is a shocking event and means they will never again be seen in their original state."

Det Insp Hart said: "The tiara, quite apart from its monetary worth, was part of the nation's history.

"Its loss is tragic. It became a personal mission to find out who had done this.

"Me and a colleague have put off retirement, we were so determined to see it through."

But even more than the loss of an heirloom, the raid led police to crimes far darker and more violent.

In footage he took of the tiara, Cumberpatch could be heard saying "I'm proper into that"

Initial inquiries pointed to a man who was already well-known to police: local man Ashley Cumberpatch, who had been arrested for firearms offences more than 12 months before.

One of the items found at this arrest - but not linked to any crime at the time - was a GoPro camera showing video footage of him accompanying a child around the Welbeck estate.

This showed him walking around the gallery and nearby grounds, including the rear windows and tiara display.

"That footage, when we looked at it, we considered it to be some reconnaissance done by the suspect," said Det Insp Hart.

"It was deliberately targeting access points, the gallery and the tiara itself.

"That gave us significant lines of inquiry very early on; it was key."

A diamond tester was seized from what police described as a burglary kit

With Cumberpatch arrested, an examination of his phone showed calls to other defendants, including Kurtis Dilks, before and after the burglary.

Police also searched a number of addresses with links to Cumberpatch, including one property in Dove Street, Nottingham.

Here they found Andrew MacDonald, who was in possession what police described as a burglary kit, including cable ties, handcuffs, lock picking equipment and - with the significance lost on no-one - a diamond testing kit.

Kurtis Dilks was found guilty of counts of conspiracy to commit burglary and robbery by the court

MacDonald admitted a series of drug offences and while in custody police examined his phone records.

Police noticed numerous calls to the Hatton Gardens area of London. A place famous for its jewellery stores.

In cooperation with the Met, they zeroed in on a business called Paris Jewels, and raided the premises in May 2019.

Here Sercan Evsin and Tevfik Guccuk were arrested.

The court heard it is thought the tiara and brooch were taken out of the country by Guccuk to his native Turkey after they were dropped off at Paris Jewels.

Tevfik Guccuk's own CCTV showed him examining items taken from the home of footballer Tom Huddlestone

Remarkably, officers found £500,000 of jewellery and watches in a cheap plastic bag.

This was initially assumed to have been from a local burglary but the presence of an FA Cup runners-up medal provoked particular interest.

Det Insp Hart said: "Our inquiry team actually discovered it was the property stolen from a tie-up robbery at Caythorpe, involving Jo Dixon, the partner of footballer Tom Huddlestone, and her son.

"So actually we recovered the jewellery from the burglary in Nottinghamshire in Hatton Garden.

"That really blew the case open; that was our golden nugget."

Tom Huddlestone, who played for Derby County at the time, was away when the burglary took place

The Caythorpe robbery had taken place in May 2019, six months after the tiara theft.

Ms Dixon had been alone at the family home, while her husband was playing an away match, in bed with her infant son, when two men in balaclavas in entered her bedroom.

They forced her to lead them to safes, before making her put her son down on the bed so they could tie her hands behind her back.

They eventually left with £500,000 worth of jewellery and handbags, including her wedding and engagement rings.

It became clear high-value burglaries in the Midlands were followed by MacDonald and associates travelling to Paris Jewels.

These burglaries followed a rough pattern where a gang would plan to use a ladder to get into first floor windows and then use threats and violence to force householders to hand over items.

But each one had its own shocking details.

The gang leaving the house of Martin Wardle after subjecting him to a terrifying ordeal

One, at the Carlton home of businessman Martin Wardle, saw the gang ambush the homeowner as he returned late at night.

Forced inside, he and his wife were bound with cable ties and Mr Wardle had his right earlobe cut with wire clippers to extract information about his valuables.

Unhappy with the amount they found, the gang then forced him, hooded, on to the back seat of his car and drove him to his mother's house in Nottingham's Park area.

Here they ransacked the property before dumping Mr Wardle back at his house.

"Throughout this time they were threatening to kill him, assaulting him and told him not to call the police because he was being watched," said Det Insp Hart.

"It is upsetting and shocking. It is wholly unnecessary violence as he and his wife are restrained and cannot offer any resistance."

Despite being challenged, the gang smashed their way into Ashley Cole's home and threatened the family

Highest profile of all was a raid on the Surrey home of former Arsenal, Chelsea and England footballer Ashley Cole in January 2020.

The gang were spotted on CCTV and warned the police were being called.

Despite this they smashed their way into the house, bound Mr Cole and his partner with cable ties and threatened to chop off his fingers if he did not give them valuables.

Police said Ashley Cole "absolutely thought they were going to kill him and his partner"

"It must have been so traumatic for Mr Cole and his partner.

"They could hear these people coming up the stairs, they had their children in their arms," said Det Insp Hart.

"The gang knew the police were coming but in that time they threatened Mr Cole.

"He absolutely thought they were going to kill him and his partner."

Cable ties used to restrain Mr and Mrs Cole had provided a vital DNA clue

But each attack provided crucial evidence. Cable ties and a knife at Mr Cole's house had DNA that was traced to Nottingham man Kurtis Dilks.

He was also linked to a folding ladder found at the home of Mr Wardle.

Now, three and a half years after the theft of the tiara and after a trial lasting almost two months, Cumberpatch, Dilks and their accomplices have been convicted for their part in the crimes.

"You absolutely have to consider them as dangerous," Det Insp Hart said. "They were armed with knives, which they held to one victim's neck.

"They have cutters, they have gone into these addresses armed with a sledgehammer.

"They have threatened, and indeed carried out, some serious violence."

But the story may not end there. Not all of those involved have been caught and police are still appealing for anyone with further information to come forward.

And of course, the tiara has never been recovered.