The source of comedy Rivers . .

'HOW f***ing lucky am I to be still working . . . still viable at this age?" demands Joan Rivers, before continuing, "I was working on my birthday. No cards, no presents."

She doesn't mention whether the work was on her forthcoming book (on plastic surgery), her autobiographical play, her new hour of stand-up, a TV guest appearance, her now famous residence on QVC or the TV pilot she is making between August in Edinburgh and September in London. Who knew there was enough space to wedge a TV pilot? Only Rivers. I suspect she may be part Time Lord.

Currently appearing in A Work In Progress By A Life In Progress at the Udderbelly Pasture, Rivers doesn't dwell on numbers. Not even numbers like 75.

"If you start thinking about how old you are . . ." her voice trails off, her eyebrows rise meaningfully (yes, they can) and her tiny shoulders shrug.

"I hate what age has done to some of my friends," she says. "They've . . ." she searches for the perfect description and finds it, "settled".

Rivers has never settled. Her schedule makes God look like Keith from EastEnders – six days and just one lousy world to show for it? On the seventh, Rivers would have played the Palladium.

This is her fifth decade in 'the business' and while this era has taken the rest of the world from Flower Power to bio fuel, Rivers has grabbed it by the decades and left it open mouthed in admiration.

Tracing the comedy Rivers to its source takes us to 1949 when, at the age of 16 and already an enthusiastic entertainer of family and friends, Rivers' mother took her to see Lenny Bruce live.

Rivers doesn't really do 'heroes' or 'influences', but she was and remains in awe of Lenny Bruce.

"He was telling it like it was" she says with no little passion. "And his stuff was so clever."

She also calls Richard Pryor a 'god' and is a fully paid up member of the Woody Allan and Howard Stern fan clubs.

"Stand-up comedy," she says "is not really a woman's field. When you go out there, you are a lion tamer." Rivers has famously declared, "There is not one female comic who was beautiful as a little girl." The women who succeed, she muses, are "mainly lesbians."

Rivers' pixie features disappear momentarily into a paper Café Nero beaker, then we take a canter through the career of a woman who was recently described on the Hollywood website Defamer as "a funny old broad with a potty mouth" and more impressively, "What Richard Pryor is to black comedians, Joan Rivers is to snarking at celebrities".

WARNING: if you have had any serious work done recently, face-wise, perhaps you should leave this section until the stitching has healed, because Joan Rivers, the life, is jaw-dropping stuff.

Rivers began as a publicist for a New York department store, married a nice, rich, Jewish boy and ended the marriage six months later.
She left home to become a straight actress, playing, inter alia, a lesbian opposite Barbra Streisand and in Juno And The Paycock, with an Irish accent which definitely presaged a career in making people laugh.

By the early 60s she was playing nightclubs, coffee houses and strip joints and seven years of standing up earned her the right to sit down as a regular guest on the legendary Johnny Carson and then Ed Sullivan shows.

Still in the 60s, she wrote for the Ed Sullivan Show, recorded a comedy album, appeared in the iconic Burt Lancaster movie The Swimmer and got her own syndicated chat show, That Show With Joan Rivers.

In the 70s, a household name, she moved to LA, wrote and starred in her first Broadway play Fun City, created a TV drama series, wrote and directed a movie with Billy Crystal (Rabbit Test, before its time, was about a man getting pregnant) and, along with the late great Zero Mostel and Gene Wilder voiced The Adventures of Letterman, a spoof superhero animation.

Rivers began the 80s headlining in Las Vegas, polishing the Grammy she won for her album, writing books, turning out TV specials and, in 1983 becoming the first ever permanent guest host on NBC's The Johnny Carson Show.

In 1986 Fox Network launched River's own, chat show, Late Night With Joan Rivers, in direct competition with Carson. A couple of well orchestrated press conferences portrayed her as biting the friendly Carsonian hand that had had fed her – and it turned round and knocked her out.

The show lasted one season and Rivers in Hollywood became about as employable as Gordon Ramsay in the Diplomatic Corps.

In the months that followed, her marriage broke up and her husband, the co-architect of her career, committed suicide. When that news came, she was in surgery. Liposuction.

"I had killed Edgar as surely as if I had pulled a trigger," she wrote, in 1991.

Rivers' determined return from that, the kind of nadir that very few have to contend with, makes Lassie look like a quitter. Three months after Edgar died, she was onstage in Vegas and her tragedy had become her comedy.

"My routines come out of total unhappiness," she has famously said, "My audiences are my group therapy."

In 1988 she went back to Broadway in Neil Simon's Broadway Bound and by the time the 90s started she had her own chatshow again, which was heading for a raft of awards.

Financially the 90s crowned her the Queen of TV Shopping. "I made it cool to appear," she says. "Now I go to record and they're all there." Small wonder, when Rivers and QVC have reportedly grossed an extremely cool half $billion.

Her books sold, she became the favourite guest velociraptor on TV both sides of the Atlantic and her play was nominated for a Tony. Sally Marr and Her Escorts was written and performed by Rivers and was about the mother of her first 'love' – Lenny Bruce.

The 90s also put her on Oscar's Red Carpet. Her trademark, "Who are you wearing?" became not so much a question as the introduction to a verbal evisceration. And the world loved it.

Now Rivers pretty much has the entertainment world at her Manolo-clad feet. And every Wednesday that she is at home in New York you will find her onstage at The Cutting Room, a little bar in Manhattan, doing stand-up. She is probably one of the naughtiest things in The Noughties.

"The only good thing about age is that it has liberated me in my stand-up. I wish I could have been this fearless when I started," she says.
How has her act changed over the years, I want to know. And is there anything that has always been in it?

It becomes apparent that the main constant in the Rivers' career has been her love of pushing the boundaries of, well, of everything, really.
In the 60s she was the first to do gay gags and to include material about married men and extramarital sex.

"I used to talk about having an affair with a married man and realising he wasn't being faithful when his wife got pregnant," she shrugs "It was shocking then."

In the 70s she got political, and personal – going for the politicians' private lives and families.

The 80s took Rivers, in the words of her agent to "places you should not go." Gynaecology. With that and the material that came out of her husband's death, Rivers' comedy went so near the bone you could almost see the marrow.

Stand-up Joan in the 90s was about plastic surgery and sex. Again, the Von Fursten-berg clad vanguard of honesty on the nip'n'tuck front.

And now? She has, she says, gone back to politics, lambasting the politically correct and the 'celebrity' greens. She has friends she says, inching forward in her seat, who boast about the Smart car they have bought – to drive to their private jet.

Celebs and sex, her own advancing years and the toll they are taking upon her physicality . . . it is all in the septuagenarian's set and some of the most breathtakingly brave is onstage in The Cutting Room.

Her material on 9/11 makes Doug Stanhope sound like Des O'Connor.

But one thing never changes: "The money is always lousy," she sighs, "they always tell me it's a career move. A career move ? I'm 75 years old, I've been doing this for 40 years. When am I going to find something I can do?"

To paraphrase one of the most wonderful people I have met, "How f***ing lucky" are we that this glorious, funny, talented woman is still "working, still viable"?

• Joan Rivers: Work In Progress By A Life In Progress, Udderbelly's Pasture, Bristo Square, until August 25, returns only, 0131-556 6550