Howard Marks has joked that he "failed" as a drug dealer as he hosted a star-studded concert weeks after revealing he is suffering from inoperable cancer.
The 69-year-old former dope smuggler-turned author appeared on stage at the Howard Marks and Friends event at The Forum in Kentish Town, north London, to raise funds for his treatment and celebrate his life.
Wearing a T-shirt bearing his alias Mr Nice, the Welshman received a rapturous reception from the audience, performing a light-hearted routine about applying to become a drugs tsar for the Government after he was released from prison.
Marks served seven years after he was caught by the US Drug Enforcement Agency.
He told the audience: "When I was released from prison I made a promise to myself that I would do whatever I possibly could to re-legalise marijuana.
"I tried all sorts of stuff. I failed as a dope dealer - a successful one gets away with it - and failed to re-legalise marijuana."
Marks, dubbed "the most sophisticated drugs baron of all time", worked for the British Secret Service after graduating from Oxford where he earned a degree in nuclear physics and post-graduate qualifications in philosophy.
He was arrested in 1988 by the American Drug Enforcement Agency and sentenced to 25 years at America's toughest federal jail, Terre Haute, in Indiana.
After being released on parole in 1995, he campaigned for the legalisation of cannabis.
Last month Marks revealed he had bowel cancer, adding that he had "no regrets" about his life.
As he sipped his drink, he told the audience: "It's funny - when you are being treated for cancer the two things you are allowed are alcohol and tobacco."
He left the stage to loud applause after around 20 minutes.
Actor Rhys Ifans, who played Marks in the 2010 film Mr Nice, Welsh band Super Furry Animals and singer-songwriter Cerys Matthews also appeared.