True Stories: Joan Rivers - A Piece of Work, More4

Thus Joan Rivers explained her continuing compulsion to keep finding stages to perform on at the age of 75, whether it was a dingy club in the Bronx at 4.30 in the afternoon, the Comedy Central Roast where she was pelted with "hilarious" insults by fellow comics, a gig for the Betty Ford clinic in Palm Springs, or somewhere in frozen Wisconsin reachable only by the kind of aircraft they use to rescue people stuck down crevasses.

At the last mentioned venue, Rivers was assailed by an audience member (male) who took exception to her joke about deaf people. She responded with extreme force, hosing her opponent with a metaphorical flame-thrower: "My mother is deaf, you stupid sonofabitch... Let me tell you what comedy is - comedy is to make everybody laugh at everything and deal with things, you idiot... 9/11 - if we didn't laugh where the hell would we all be? Think about that!"

It was the fear and desperation behind Rivers's comedy that drove this film, as presumably it has driven her throughout her career. For all the movies about the cynicism, cruelty, substance abuse and insanity of the showbiz life, I can't remember seeing the cost of being a performer brought home with such gut-kicking force. It was as if every performance - or at least all the history and struggle and middle-of-the-night travelling that went into every performance - took a few new chunks out of Rivers, and, like health insurance, the longer she kept doing it the higher the premiums climbed. It shed new light on her fabled fixation with plastic surgery - if she didn't keep getting her face rebuilt, there'd be nothing left by now except a screaming skull.

Joan showed us her beautiful New York apartment - "This is how Marie Antoinette would have lived if she'd had money" - but everything she has to show for her life's work has been paid for several times over at an exorbitant rate of interest. "Age?" she rasped. "It's the one mountain you can't overcome. It's a youth society and nobody wants you."

It was telling that the film had been made by women, co-directors Ricki Stern and Annie Sundberg, because the way Rivers told it, men had never been terribly keen on seeing her succeed. She recalled how they'd been disgusted when she did routines about abortion or the casting couch, and warned her she was straying into areas that should remain off limits. Her career received a huge boost from an endorsement by Tonight Show host Johnny Carson, for whom she became the permanent guest host, but when she accepted an offer from Fox to front her own show, a furious Carson had her blacklisted at NBC. The Fox project ended in catastrophe, when the network axed Rivers and her husband Edgar committed suicide. "This business, you're unloved your whole life," she lamented, straying momentarily into something like self-pity.

She describes herself as an actress who plays the role of a comedian, but the distinction must be lost on her audiences. Bottom line? She's obscenely, paint-strippingly hilarious: "I love anal sex, cos you can do other things! You can iron, you can read a book, get your emails on your BlackBerry..." And she's dogged and driven enough to understand that what goes around comes around. "Nothing is yours permanently and you'd better enjoy it while it's happening," she soundbit, having just won Donald Trump's Celebrity Apprentice show. It's like her agent Larry Thompson says: "You have to stay out in the rain to get hit by lightning."