Who killed Kenneth Williams?

He did, suggests a new film starring Michael Sheen. It was an accidental overdose, say friends. Who is right?

He was one of our best-loved comedians, an icon of end-of-the-pier fun, but behind Kenneth Williams's comically flared nostrils and haughty sneer was a deeply troubled soul.

At the time of his death in 1988, no one outside his small circle of friends had an inkling of his torment. So when he was found dead in his flat at 62, it was generally assumed that yet another comedy great had slipped away prematurely.

But with the posthumous publication of his diary in 1993 questions began to be asked. Now a new BBC film will rekindle the debate about whether the star of 22 Carry On films took his own life or whether his overdose was simply a terrible mistake.

Fantabulosa will be based on the private thoughts Williams recorded throughout his life. He first referred to himself as a "suicidalist" in his twenties, and often wrote of his desire to end it all, reaching a peak during his last few months. But his friends have long refused to believe it. They argue that he would not have bowed out without making arrangements for his beloved mother, Lou, who lived in an adjacent apartment near Regent's Park. She received none of the £500,000 he left in his will.

Williams was an enigma. Alongside his Carry On roles, he notched up countless appearances in the radio comedies Round the Horneand Beyond Our Ken, as well as on TV's Hancock's Half Hour. He opened the door to a tidal wave of camp comics. But, away from the public gaze, he was racked by his homosexuality, what he saw as the demise of his career and unbearable stomach pains. The latter stages of his life were seen out on the chat-show circuit.

Just months before he died he wrote: "All that is on my mind now is the way to commit suicide: it has got to be efficient and in a place where nobody is inconvenienced." His final entry detailed his pain and concluded with the words: "Oh, what's the bloody point?"

Ben Evans, producer of the new film, to be shown on BBC4 next year, says: "We've tried to put down everything we know about his last day. He was suffering tremendously from pains in his stomach and back, and he couldn't stop the pain."

Michael Sheen, best known for his performance as Tony Blair in Channel 4's The Deal, will play Williams. "I go along with what Miriam Margolyes [a friend of Williams] said: I believe Kenneth killed himself, but I don't know for sure," said Sheen, who has lost two and half stone for the role.

Those close to Williams maintain, however, that he did not take his own life. But many, such as Barbara Windsor, his Carry On co-star and a close friend for many years, remain deeply distressed about his death and are unhappy speculating about his final days.

A former companion of Williams, Paul Florance, has said: "The absence of a farewell letter to me after we had been lovers, friends and prolific letter writers for 20 years leaves me in no doubt his death was an accident."

The writer Russell Davies, who edited Williams's published diaries, says: "I think you would be hard pushed to find any friends who thought it was suicide, but having looked at the diaries, it is hard to come to any other conclusion."