The late Queen’s phrase “recollections may vary” is something documentary-makers know all too well as they try to tell real-life stories.

In the case of new BBC two-parter Hunting Mr Nice: The Cannabis Kingpin, an added challenge was that several of the interviewees were frequently high on drugs during the times they were trying to recollect.

The audience at the RTS Cymru Wales screening and Q&A learnt about the difficulties of assembling and questioning members of notorious cannabis smuggler Howard Marks’s inner circle, some of whom had never spoken before.

Gwenllian Hughes, founder of Kailash Films, who directs the series with Nick Leader, said: “Half the contributors would have been stoned for most of the years with him. Their memories were all slightly different, so we had to feel our way through.

“It was challenging to find these people to talk to. I really wanted to get one guy who had known him since university but who had never spoken before. While putting out feelers, everyone said he had died, so I gave up.

“Then one night at 10.00pm my mobile rang and a voice said, ‘This is Brian.’ He had faked his own death so he could live a normal life. I spent a month getting him to take part, anonymously. He would turn up to meetings in disguise – it was crazy.

“It’s what film-makers live for, these untold stories, and it felt really special. But it was also a massive pressure. We set up the filming, really hoping he would turn up, and he did. He told us everything then just disappeared without saying goodbye.”

Hunting Mr Nice: The Cannabis Kingpin, a co-production between Passion Pictures and Kailash Films, aired on BBC One Wales and BBC Two in late November. It tells the story of the charming Welsh criminal who smuggled tens of millions of dollars’ worth of cannabis across the globe. The Oxford graduate was a master of disguise with up to 43 aliases, including Donald Nice, hence his nickname.

“Film-makers live for untold stories”

Law enforcement agents tracked him for years before he was eventually caught. He served seven years of a 25-year sentence in the US and, on release, campaigned passionately for the legalisation of cannabis. He died of cancer in 2016, aged 70.

The cleverly crafted documentary brings together for the first time Marks’s inner circle and the agents involved in the cat-and-mouse pursuit.

BBC Wales commissioner Julian Carey said: “Howard holds a unique place in Welsh culture and is still part of the landscape. He’s a charming chameleon; cheeky but a criminal with a weird Robin Hood good guy/bad guy personality. We wanted to get a Welsh character and story on a national network and to show people different parts of our country and culture, even ones as dodgy as Howard.

“No one died, it’s not awful, but we wanted to ask how nice was Mr Nice? We explore the consequences and the darker parts of his criminality.” Former BBC Wales journalist Penny Roberts had interviewed Marks about the effect of his actions on his family, who he called “unnecessary casualties of the insane war on drugs”.

Executive producer Hamish Fergusson, Creative Director at Passion Pictures, added: “People are conflicted by him. Even DEA agent Craig Lovato, who spent years hunting him, is full of a curious affection for Marks. We can be charmed by him and still know what he did. We leave it to the viewers to form their own opinions of him.”

‘Hunting Mr Nice’ was an RTS Cymru Wales event with BBC Wales and BBC Factual. It was held on 18 November at the University of South Wales Atrium in Cardiff, hosted by Radio 6 DJ Huw Stephens and produced by Michele Marsland.