Click here to watch a sketch from Hancock's Half Hour

Click here to watch the classic sketch The Blood Donor

A comic genius cuckolds his best friend, a gentle actor beloved by the nation. The actor's young wife discovers undreamt-of passion in the comic's arms, then watches helplessly as alcoholism and thwarted ambition destroy him. She finally learns of his suicide in circumstances so tragic that they could have been devised by Thomas Hardy.

This is not some tragic romantic fiction, but the painfully real story of Tony Hancock and his affair with Joan, the wife of his best friend John Le Mesurier. It is retold, without a whiff of sentimentality or melodrama, in Hancock and Joan, a poignant new play by Rick Cottan. Ken Stott plays Hancock, Maxine Peake is Joan and Alex Jennings the long-suffering John.

Following Fantabulosa!, its superb but excruciating 2006 Kenneth Williams drama starring Michael Sheen, BBC Four has made a season of dramas about the tortured lives of 1960s comedy icons. Jason Isaacs and Phil Davis kick off as Steptoe and Son (Wilfred Brambell and Harry H.Corbett); David Walliams is Frankie Howerd; and Trevor Eve plays Hughie Green.

Not all clowns shed bitter private tears - think of those cheery surviving Pythons - but this menu promises a banquet of anguish: desperate gay predation, adultery, betrayal and mutual hatred, and lashings of self-loathing all round.

Cottan based his script on Lady Don't Fall Backwards, Joan's account of the affair published in 1988 (John had died in 1983). He interviewed her in her handsome Ramsgate home, full of mementoes of both the men she loved. When we talk, Joan is extraordinarily spry, jolly, open and disarmingly frank about her relationships. At 76, she still has the kind of raunchy laugh that would have done justice to Sid James in a Carry On film.

“The attraction was very strong and instantaneous,” she tells me, recalling the day that her husband first brought Hancock to their home. “I'd been married before, but this was the first time I'd been head over heels in love.” I mention that her book implies that Hancock had strong sexual charisma. “Definitely!” she says with that earthy laugh. “Very strong! But he was also very vulnerable. He brought out my maternal feelings, and he was always so funny, even in the depths of depression.”

Joan had been working at the Establishment, Peter Cook's satire club, when she met John. His wife Hattie Jacques was leaving him for a younger man, and Hattie herself set John and Joan up on a date. “He was still desperately unhappy about Hattie,” she recalls. “He was completely helpless. He couldn't even boil an egg. Once when I was ill he tried to make me a cup of tea and he put the tea straight into the kettle. He had exquisitely good manners but he was like a lot of public schoolboys then, completely undomesticated. Even when I'd gone to live with Tony, I used to pop home to pay the bills and organise the cleaner.”

Hancock was depressed about the collapse of his marriage to his second wife, Freddie, when John brought him home. “With Tony it was the first time I'd been completely swept off my feet,” she says “Physically, it hadn't really happened between me and John. He was the first to admit that right to the end.” In the first flush of the affair, she and Hancock wanted to have a baby together, she tells me. “We weren't lucky, but we had a lot of fun trying!” That laugh again.

She quickly learnt two things about her new lover. The first was that he was desperate to be recognised as a comic genius on his own. “He wanted to be like his idols. He loved Buster Keaton, Jacques Tati and especially Sid Fields,” she says. “He did a marvellous imitation of Sid Fields. He made me laugh and laugh and laugh.” He had gradually ousted characters from his radio and television show. “Kenneth Williams was particularly bitter about that,” she says. “Vitriolic!”

By the time they met he had jettisoned Sid James, desperate not to become a double act. “I once told him he was very funny with Sid. ‘Did you like The Blood Donor?' he asked me. ‘Yes,' I said. ‘Well Sid wasn't in it!'” Finally, he abruptly dumped his writers, Ray Galton and Alan Simpson, claiming that they got all their material from him anyway, listening to him holding forth in the bar. “It was disastrous,” she says. “I wanted him to give up the business and become a farmer or a plumber, anything, but he couldn't and wouldn't.”

“It's so common,” Cottan, the writer, reflects. “A great performer spends half his life trying to get rid of the character who has made him famous, without realising that that character is him, and that's what the public love him for.”

Joan's second lesson was infinitely harder. “Tony sounded much more upper-class than his comedy character,” she says. “He was a strange mixture, very economical sometimes and flamboyantly extravagant, always staying in the Maharaja Suite at the Mayfair Hotel. And he loved fine wines.” But she soon discovered that wine was the most innocent of his tipples.

“At first I was very naive about his alcoholism, but I soon learnt to read the signs. When he was supposed to be drying out he was very cunning and deceitful, as alcoholics often are. He'd suddenly say he was going to the shops, which he never did. Once he said he was going to join the library at seven at night!”

Although Hancock had been occasionally violent with his previous wives, Joan tells me he never hit her, lashing out with his tongue instead. “You had to keep him off the brandy if at all possible. It made him really nasty.” Hancock himself called it “the old infuriator”. Joan says Hancock's mother, Lily, warned her not to take him to France, and, if they did go, to make sure he stayed off the cognac. The drama opens in the aftermath of an incident when Hancock drank a whole bottle in five minutes at his mother's home and collapsed.

“When he came round from the coma the doctor asked: ‘Do you want to die, Mr Hancock?', and he said ‘Yes',” Joan recalls. “I was really hurt by that.” Her father had been “a big Hancock buff”, she says, but in a drunken outburst he called her mother “a parochial Mancunian c***!”. After that they would have nothing to do with him.

Cottan has deliberately omitted some of his strangest antics in case the play became too dark. Joan recalls one New Year's Eve when, under the influence of prescription drugs, Hancock wandered into the ballroom under his Pimlico flat dressed only in a candlewick bedspread and wearing a G-string, back to front. “He walked up to a woman, who screamed, and said: ‘I bet you've never seen one of these!'”

Unable to cope, Joan went back to the ever-forgiving John, but the affair resumed in secret shortly before Hancock left for Australia and his bid for international stardom. “I told Tony that if he stayed dry for a year I would leave John and marry him.”

This is where Thomas Hardy seems to hijack the plot. Hancock's show was not going well. He became depressed and hit the bottle. He wrote to her every day. She got his letters but a postal strike in Australia meant that he never received her replies. She could never get through on the phone and, because the resumed affair was still secret, she couldn't leave messages. He couldn't ring her house in case John answered.

When she was cited as corespondent in Hancock's divorce case, Joan told the press the affair was over. He saw the reports in the British papers and believed them. The night before he died he rang Lily in desperation. Lily rang Joan's parents, who told her that Joan was in Rome with John and wanted nothing to do with him. Lily relayed this to Hancock, who believed he had lost her. The night that Joan returned from Rome was when Hancock was taking the pills.

“It took me a year to get over the grief,” she says, but she stayed with the kindly and ever-forgiving John until his death in 1983. She insists that it remained a happy marriage in its way. “He was always my confidant,” she says, even during the affair with Tony. They both had occasional flings with other partners, she says, but nothing that would endanger the marriage. “What, John too?” I ask. He was away filming a lot, she says, and people would offer themselves “but he was very well mannered, and I think he was too polite to say no.” She suffered some criticism when she wrote her memoir five years later, “but I think it's a jolly good story,” she says. Now she lives in her handsome Ramsgate home surrounded by mementoes of the two men she loved.

And watching the drama? “It was uncanny,” she says, “very emotional. At first I was a little nervous, but Maxine Peake was excellent. Ken Stott was so Hancockian! The walk, the body, the movements: all perfect. It was like a stab to the heart.”

Hancock and Joan is on BBC Four on March 26. The Curse of Comedy season begins on BBC Four on Wednesday at 9pm with The Curse of Steptoe

STONE ME! SIX WAYS IN WHICH TONY HANCOCK WAS A STAR

The streets of Britain would empty whenever one of the 100 episodes of Hancock's Half Hour was on the radio from 1954-59. Mixing flights of fancy with dowdy detail - in one of the most famous episodes, A Sunday Afternoon at Home, nothing really happens - it helped redefine British comedy. Co-stars included Kenneth Williams and Sid James.

The show moved to television in 1956. Hancock and James went on to share their house (23 Railway Cuttings, East Cheam) for six series in which our Homburg-wearing hero offered a mix of grandiloquence and gloom that was gloriously offset by James's blokish scheming.

His peerlessly expressive face made him a national icon - he appeared in the famous “go to work on an egg” TV advert, and was the first actor to be paid £1,000 for a single sitcom.

Fearing he had become half of a double act, Hancock got rid of Sid James in 1960. The subsequent series featured the classic episode The Blood Donor, which gave Hancock his immortal line: “A pint? That's nearly an armful!”

He made two films: The Rebel (1960) and The Punch and Judy Man (1962). Neither was a hit.

In a poll for BBC radio in 2002, Hancock was voted the greatest comedian ever. Fans include Pete Doherty, who named the Libertines' album Up the Bracket after one of his catchphrases.

Dominic Maxwell

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