Image caption Howard Marks now lives in Leeds, closer to family

At one time he was one of the world's most wanted men. Howard Marks spent years in a tough American prison, but these days a one-bedroom flat in Leeds houses the drug-smuggling author and campaigner.

When I visited him the heat was stifling.

Marks explained that the thermostat was set high to take away the chill that he feels as a side-effect of his treatment for cancer.

"It's a terminal disease. Obviously a medical miracle can happen at any time, so fingers crossed for one of those," he said.

"I do tolerate chemotherapeutic drugs very well, the tumours are decreasing. But there's no chance of them going away."

With a characteristic grin and with his deep Welsh drawl, Marks, 70, tells me the doctors have allowed him to carry on smoking. But it seems he's finally given up on cannabis.

"I took about eight weeks' supply of cannabis oil, the strongest possible, in one hit. Along with everything from apricot seeds to moths, all the crazy crackpot anti-cancer things you can take. People start peppering you with what works, and what doesn't.

"I just took the lot and got sectioned, and put in the nut-house for two weeks."

Image copyright Getty Images

Howard Marks

1945 : Born in Kenfig Hill, Bridgend

: Born in Kenfig Hill, Bridgend 1967: Degree in physics at Balliol College, Oxford

Degree in physics at Balliol College, Oxford 1970: Begins dealing in cannabis

Begins dealing in cannabis 1988: Arrested in Spain on trafficking charges and extradited to the United States, where he is jailed for 25 years.

Arrested in Spain on trafficking charges and extradited to the United States, where he is jailed for 25 years. 1995: Released on parole for good behaviour after serving seven years.

Released on parole for good behaviour after serving seven years. 1996: Publishes Mr Nice, his autobiography. Super Furry Animals' debut album features track Hangin' with Howard Marks and a montage of Marks' passport photos on the cover.

Publishes Mr Nice, his autobiography. Super Furry Animals' debut album features track Hangin' with Howard Marks and a montage of Marks' passport photos on the cover. 1997: Starts touring his one-man show discussing his life and views on drugs; stands in four parliamentary constituencies in the general election on a legalise cannabis ticket

Starts touring his one-man show discussing his life and views on drugs; stands in four parliamentary constituencies in the general election on a legalise cannabis ticket 2006: Publishes Senor Nice, a sequel.

Publishes Senor Nice, a sequel. 2010: Rhys Ifans plays Marks in the film version of Mr Nice.

Rhys Ifans plays Marks in the film version of Mr Nice. 2015: Marks reveals he has been diagnosed with cancer. Publishes his latest book, Mr Smiley: My Last Pill and Testament.

Thirty years ago Marks was at the centre of a manhunt. He was the criminal mastermind who police said was at the centre of the world's biggest cannabis deals.

Dubbed the "Marco Polo of the drugs world", his smuggling exploits eventually ended when he was extradited from Spain to America to stand trial.

In 1990 he was jailed for 25 years. Inside, he was a model prisoner and in 1995 he was released on the grounds of his good behaviour.

He went on to write the bestseller, Mr Nice, chronicling his life on the run and in prison. And he became a passionate campaigner for the legalisation of cannabis and other drugs, a cause he still supports today.

"Pretty much every drug would be safer to society if legalised and controlled, rather than left up to the criminal fraternity, which seems to be the choice of government - it's only like this because they want it like this.

"Of course one has to have the caveat that if a drug is discovered or synthesised that makes you want to kill people and rape people, then make it illegal, obviously.

"I haven't taken every drug in the world, but I've taken a lot, and I haven't come across one that makes you like that. Except possibly alcohol, which is the only one that's legal. So none of it makes sense to me."

Media playback is unsupported on your device Media caption Archive from 1988 when Howard Marks was arrested in Spain - and speaking from prison in the US

Image copyright FRANCOIS GUILLOT/Getty Images Image caption He turned to writing and acting after his release from prison

Image copyright Ian Gavan/Getty Image caption Rhys Ifans with Marks at the premiere of Mr Nice in 2010

After meeting Marks it is easy to see how he charmed his way out of difficult situations. He has courted a reputation as a "principled" drug smuggler, and his new book, Mr Smiley, contains the same jovial attitude towards a world that many others would consider to be dangerous, damaging and - at its heart - a hive of criminality.

'Contaminated'

In his book, and in his interview with me, he admits that he returned to his old ways after his release from prison. But it was the party drugs of the 1990s that caught his attention.

"My involvement with ecstasy was mainly testing it outside clubs - putting a lab coat on, making sure it was alright. That was the non-smuggling involvement, and then I'm afraid I got a little bit interested in making money out of it."

Marks insists he made no money from the deal after realising he had obtained a rogue batch of the drug.

"I had a strong reason to believe that the ecstasy I had at my disposal was contaminated, and that's the danger with non-cannabis. You can tell with cannabis, it grows in the ground. But with pills, you have no idea what's in them."

If those who oppose Marks' outspoken stance on drugs were hoping for a hint of regret, they will be disappointed.

While he admits to having felt occasional regret in the past, he says he is happy with life and he has learned to live with his cancer diagnosis.

Judging by his surroundings in Leeds, the millions he is said to have made in the 1970s and 1980s have gone. Limited funds, and the shortage of time he has left, led to him writing the latest volume of his memoirs.

Not all of the reviews for his book have been positive, but his cheerful attitude allows him to take the feedback on the chin.

"One of the reviews on Amazon says 'yeah, the general information bits are OK but then he devolves to his usual drivel'," he chuckles. "Very unkind!"