There is an oft-quoted assertion about the gold from the Brink’s-Mat robbery of 1983, in which six men in a van set out to steal £1m in cash from a Heathrow warehouse and instead made off with bullion worth £26m: if you have bought gold jewellery in Britain since 1984, it is likely to contain traces of the Brink’s-Mat haul.

In other words, there was a lot of it. Which is good news for fans of The Gold, Neil Forsyth’s hit BBC drama about the robbers, as well as the dogged police team who pursued them, because it means there’s plenty of rich material for series two.

Two years ago, the first series – which drew a big Sunday evening audience and was nominated for a Best Drama Series Bafta – concluded with multiple convictions for some of those involved in the robbery and handling of the gold, but also with the police realising they’d only ever been hunting half the stash.

The second series, airing from 8 June on BBC One, explores theories as to what happened to the rest. At an RTS preview screening, writer Neil Forsyth explained why he went back to the tale. “There’s a natural division within the story into two halves. There’s a not hugely subtle ending to the first series that begets a second series. It had to grow, and it gets even further from the Brink’s-Mat warehouse – but it starts there, which is important.

“It’s still the second half of The Gold, but it reaches further into the 90s, when it became even harder for the people involved to get rid of the gold, and particularly to handle the money that came from it. Business, and therefore crime, became more international. There was a recession in Britain, so the money gravitated abroad fairly quickly. It was great to send the story into new worlds and bring in new characters.”

Those “new worlds” range from Cornwall to Tenerife and the British Virgin Islands, and characters include the same mixture of real and made-up figures as series one. Stephen Campbell Moore plays real-life maverick policeman Tony Lundy, while Tom Hughes’ lawman-turned-money launderer Logan Campbell is a composite of characters Forsyth came across in his research.

Policing trio DCS Brian Boyce (the investigating officer, played by Hugh Bonneville) and his fictional detectives Nicki Jennings and Tony Brightwell (Charlotte Spencer and Emun Elliott) return for the new run. For Bonneville, knowing that Boyce was satisfied with his portrayal was important. He told the RTS: “I’ve had the pleasure of meeting him – once as we started shooting and then after he’d seen the first season. He gave a thumbs-up, so we were proud of that.

"Chop Boyce in half and you'd see police right through. He was a man of principle and integrity"

“If you chopped him in half, you’d see police right through, and doing the right thing. He was incorruptible because, unlike certain others in the Metropolitan Police and other police forces, he had not been got at by money. He was a man of principle and integrity. I love the sense that this little triumvirate is going to try and hang on to what is right, whatever they are faced with.”

Spencer’s detective stands out for her tenacious pursuit of villainy, with the character’s working-class background and criminal connections (Boyce tells her he once arrested her father) initially perceived as a flaw but increasingly as a strength. She said: “Fundamentally, Jennings wanted to do good. The police get a lot of flak, but there are people trying to do the right thing. She’s a rottweiler. In a world where we now love our anti-heroes, I’m thinking: ‘Maybe we should love our heroes again.’

“Neil wrote her as coming from that same background [as the villains in the show] but the difference was that she chose to do good; she could have gone down that path as well but she didn’t.”

One reason for The Gold’s success is Forsyth’s skill in moving the tale beyond a traditional battle of cops and robbers, and bringing out the ambitions, both noble and otherwise, of those on the wrong side of the law in the interest of bettering their station.

The first series saw Jack Lowden and Tom Cullen playing men whose country houses and lavish lifestyles were built on the proceeds of crime. This time, Cullen’s John Palmer – seen building his fortune through smelting the gold – is ruthless in expanding his empire through schemes that include the sale of timeshare holidays in Spain.

Palmer is seen as monstrous yet relatable. The actor told the RTS: “He is a guy from Solihull. He grew up next to a dump and was so poor he had holes in his shoes – so he’s driven to better himself. As we go through series two, the line between his self-betterment and greed becomes very murky. The start finds him at his zenith, running this successful timeshare business, and this season is about how greed can dismantle a person.

“As humans, we are the heroes of our own stories, and Neil’s writing constantly creates these frictions and dramas that are character-led. This isn’t just about money-laundering – it’s a human story.”

Two of the most important new characters inhabit that crucial space between cartoonish villainy and the wealth and status it can bring. Forsyth offers a complex picture of movement up the social ladder made possible by overnight wealth, this time through unethical lawmen Logan Campbell and his fellow Cambridge alumnus Douglas Baxter, played in scene-stealing style by Josh McGuire. Forsyth explained: “Money-laundering had become fairly established by the time of this series - the late 1980s and into the 1990s – and at an international level. The Brink’s-Mat money just went off into it. To throw in all these characters and these areas of criminality was very satisfying.”

It’s a big story, told through a mix of derring-do, comedy and charm alongside the ethical dilemmas, and this second series will no doubt be as successful as the first.  Which leads to the inevitable question: will there be a third? Forsyth shook his head: “Sadly, they can’t find a third half of the gold, so I’m afraid that’s your lot!”

Report by Caroline Frost. The RTS screening and Q&A with the cast and creatives of The Gold was held at the British Museum on 21 May. The producer was the BBC and Objective Media Group.