His heart beating fast, Neil Duttson pulled a black pouch from his pocket and placed it on a table in the boardroom of Goldman Sachs.

Across from him was a banker, his eyes wide with anticipation.

Neil unfastened the bag, pouring from it a cascade of 'diamonds' onto the glass surface, their sharp edges catching the light.

"Why don't you pick one?" he asked, gesturing towards the stones, which he knew were fake.

The banker, who was planning to propose to his girlfriend, chose the biggest.

"That one's £10,000, but I'm going to need a 50% deposit," Neil said, his pulse racing.

The unsuspecting banker handed Neil the cash, smiling as he pictured his soon-to-be fiancée's eyes lighting up.

Days later he met with Neil once more and was presented with the emerald-cut stone - only this time it was real.

Keen to become a big name in the world of diamonds but without the cash to get going, Neil had resorted to using fakes to get his hands on some much-needed funds.

He didn't have the money to buy the real gems up front, but with the £5,000 deposit bought the banker the genuine stone.

"I didn’t really lie and I didn’t sell him anything that wasn’t real," says the 53-year-old from Ramsgate.

"I took a deposit for something that he liked the look of, and all I did was match the bit of glass with a real stone.

"He knows the story now, and we've actually become good friends. He's been back to me over the years.

"I’m in a situation now that I own all my diamonds. It was just one of those interesting starts."

It was the first and last time Neil would pull the wool over a customer's eyes; a one-off necessity that paved the way for him becoming one of the country's leading diamond dealers.

Twenty years later, he now has a who's who list of celebrity clients and has travelled the world on his quest to find the perfect stones, rubbing shoulders with global superstars and sidestepping African warlords.

But how did the journey begin?

Neil, who owns Duttson Rocks, admits it wasn't his initial career plan, having left school without any grades and going straight into the armed forces at 17, but says he's always had a penchant for jewels.

"When I was a kid, I'd always play with my mum's jewellery," he recalls.

"She had one of those charm bracelets and the odd small diamond and emerald.

"When I left school I actually wrote to De Beers asking if they’d give me a job, but they weren’t interested as I needed two A-levels in maths and physics. So I didn’t think anything more about it."

But 12 years later, after a spell with the Marines, two ski seasons in Val-d'Isère and running his successful events company, Neil started researching diamond courses.

"I found one in Antwerp in Belgium, which is where 85% of the world's diamonds went through in those days," he explains.

"I moved into a youth hostel for six months and shared a classroom with five Sri Lankans who had signed up for this course to learn how to smuggle.

"They didn’t want to be ripped off, and you can imagine they were dealing with some dark forces trying to sell them dodgy stones, and so they had to learn the trade in order to avoid that."

After finishing the course, Neil moved back to London and wrote to journalist Lucia van der Post, associate editor of the Financial Times' How to Spend it Magazine.

"I said ‘you don’t know me, I’m not a jeweller, I’m a diamond dealer, would you be interested in chatting?’. She said 'yeah'.

"She wrote an article saying I was the new guy on street and telling people that rather than going to Bond Street, to see me instead.

"I needed to get my name out there in London, as that was the only way to do it."

But there was still one big and rather important obstacle to overcome - Neil didn't have the money to buy diamonds to show potential customers.

Instead he had to convince diamond owners to lend him their gems.

"That was the hardest thing as it’s a very Jewish and Indian industry and I am neither, so it was bloody hard work," he said.

"A guy who’s got a billion dollars of diamonds isn’t going to lend me a £10,000 stone without any payment up front."

And so it was that Neil found himself in the boardroom of Goldman Sachs with a bag of fake gems.

The money he made from that first sale was the kickstart he needed.

Through word of mouth he built up a reputation as quite the expert, spending much of his time abroad in diamond hotspots such as Sierra Leone, Angola, Namibia and South Africa.

He sourced ‘rough’ ethically - meaning with all the correct licences - travelling with an ex-Special Forces friend and a fixer in Sierra Leone, who was a former South African mercenary.

"My job was to source uncut diamonds using my expertise and training for another company," he explains.

Neil says he would find himself in African villages with no TV, no hot running water and locals who had barely ever seen a white man.

But he nevertheless won them over, in one case so much so that they named a palm tree after him. In another, one villager's first born would be named Neil.

However, while sourcing diamonds overseas, he had to be extra vigilant of the "dodgy" people trying to sell gems.

"You’re dealing with warlords," he says matter of factly. "You’ve got to be very aware and very careful.

"But what I do and what I push is ethical - I don’t buy diamonds from dodgy people, but it was a part of life that I saw."

The 80s, 90s and early 2000s saw huge problems within the industry, and the rise of blood or conflict-diamonds - those mined in African war zones by forced labour.

Funds from the process would then be used to arm rebel movements and profit warlords.

The 2006 blockbuster hit Blood Diamond, starring Leonardo DiCaprio, depicted enslaved locals harvesting diamonds to fund the rebels' war effort.

But in 2003, in a bid to stop the flow of conflict diamonds, the Kimberley Process was established, creating a certificate scheme to help oversee the industry and make it more transparent.

While Neil says things have changed, he admits some "hangovers" from the past still exist in some countries.

"Every diamond pretty much is certificated, so the average layperson can buy a diamond," he explains.

"The sad thing is there are dark forces in my industry, so where something is easy to smuggle or fake, people will do that.

"And so having a certificate for a diamond these days doesn’t mean anything really unless you’ve got someone like myself checking it out for you."

While the financial crash in 2008 dented the sale of luxury goods, Neil says everything has changed and it's very "sexy" again.

He has two world-leading suppliers - one of which is the third-largest diamond-dealing family "on the planet" - and he sources his polished stones from them.

He has clients worldwide, some who store their wealth in diamonds, and others who he creates jewellery for.

Among them are Emma Willis, Serena Williams, Frank Lampard and a number of the Made in Chelsea cast members including Jamie Laing and Spencer Matthews.

He says customers often come to him without an idea and he can help draw up the design of the ring and help them decide the cut of the diamond.

But he insists size isn't everything.

"It doesn’t matter how big the diamond is, that’s not where the money is," he says. "It’s all down to the colour and clarity.

"It’s the characteristics of that diamond, the polish, the cut, the symmetry, which is what they don’t teach when you go into a shop on Bond Street.

"What I try to do is educate everybody, my clients, and when they go home and get down on bended knee, at least they have some knowledge. It’s not just 'here’s a ring love and it cost me £5,000'.

"They can say ‘by the way, the polish and symmetry of this stone is equivalent to a Cartier stone’."

Neil's team creates the jewellery at his workshop in Hatton Garden, London's jewellery quarter and centre of the diamond trade in the UK.

"What I do is all very bespoke, it's not like walking into a shop," he explains.

"I’ll have a first meeting with the client to discuss what they would like, then the second meeting is at the workshop, where I’ll show the diamonds.

"It’s all honest fun and people love the experience of coming to the workshop."

While Neil keeps the numbers close to his chest, not wishing to reveal the large sums his clients have spent, he gives one piece of advice.

"Don’t spend what you can’t afford.

"And it's not about the size; it's the four Cs - colour, clarity, carat and cut. Don't be fooled by the bigger the diamond the better."