There is no need to worry though - old age has not suddenly kicked in for the comedy icon.

She has simply performed so many dates on tour she would rather just take in the scenery than discuss where she is.

"I am in my hotel bedroom looking across a lake and trees," Joan told me, the only journalist granted an interview with her during her current 14-night The Now or Never Tour throughout Britain.

"I love having a different surprise wherever I go and I love the glorious concert halls I have been performing in.

"I love what I do and am always excited to see new places.

"The English audiences are very warm, as well."

American Joan is, perhaps, surprisingly congenial and friendly on a one-to-one basis, considering her formidable, acerbic and no-holds-barred act on stage.

"You have to be polite and accessible to people," she said.

"I met Russell Crowe once and he was so rude, it is something I always remember.

"People remember what another person is like after they have met them.

"On the other hand, I met Meryl Streep and she was lovely - I remembered that. I have manners - it is what my parents taught me.

"Of course, there are certain things I want to say to people at parties, for instance, but I can't.

"I wait until I am on stage."

It is in front of an audience where she comes alive - and nobody is safe.

Joan's reliability to poke fun at Hollywood and celebrity culture has ensured a hugely-successful career since the 1960s.

Born Joan Alexandra Molinsky in Brooklyn, her parents, Beatrice and Meyer, were Russian Jewish immigrants.

Raised in Larchmont, Westchester County, New York, she started out at various comedy clubs, before making her name as a television presenter and a gag writer.

Mentored by American TV talk show legend Johnny Carson, she became a headliner in Las Vegas in the 1980s.

She was heavily influenced by controversial Jewish comedian Lenny Bruce.

His riposte involving race was almost unheard of in 1960s America.

"Lenny Bruce absolutely told the truth," she recalled.

"He went into areas that nobody dared talk about in the 1960s.

"I was taken to see him when I was still in college and I was in shock and awe."

These days Joan hosts copious pre-award shows and is a regular face on the red carpet, together with daughter Melissa Rivers.

She also hosts Fashion Police, commenting on celebrity fashion.

Joan, who shares a home with Melissa and her nine-year-old grandson Cooper, said: "There is much more liberty and freedom in comedy compared to when I first started out.

"Then you had all the 'my mother-in-law is so fat' gags.

"People such as Woody Allen, George Carlin and myself have changed that.

"We just talk about our lives and that is funny."

Her self-deprecating humour is evident in her most recent book I Hate Everyone . . . Starting With Me and her 2010 documentary Joan Rivers: A Piece of Work.

"I love the collectiveness of the laughter when you say something funny," Joan explained.

"To hear 2,000 people laugh is such a reward."

Nobody and no topic - no matter how taboo it may be considered - is left unturned by Joan.

On her current tour, she talks about Nazi concentration camps, Kirk Douglas' stroke, Michael J Fox's Parkinson's Disease, Jimmy Savile and outrageous stories of sex and celebrities which cannot be printed in a family newspaper.

"Look, after 46 years of performing, people know what to expect when they come to see me," she explained.

"They know it is going to be fun and outrageous.

"I have maybe one complaint every five years about my act.

"If you don't like it, you should not have come to see me in the first place.

"By telling jokes about Auschwitz, Dachau and Anne Frank, I feel I am helping to make people remember what happened.

"If someone is having a really bad time, I will make a joke about it on stage, but I won't make fun of somebody if they are in major trouble."

Even 9/11 is not off limits for the daring Joan.

"After that happened, I was the first one to start telling jokes about it," she remembered.

"Most people did not mind, I even had letters saying thank you for helping me laugh during the suffering."

There is a discrepancy over her age: She claims to be 79, but other media outlets have said she is in her early 80s.

One thing for sure is that there are no signs of slowing down.

Embarking on such a gruelling 14 night tour - complete with tour bus - would tire out someone half her age.

"Why would I stop and retire?" Joan asked.

"I love performing and we Jews are very creative.

"We have always used humour to get ourselves out of terrible situations."

Not brought up in a religious family, she said her Judaism contributed towards her coping when her husband, German-born Edgar Rosenberg, committed suicide in 1987.

"The rituals and the shiva house definitely did help, but I cannot say that religion brought me through it, even if I wished it were true," Joan recalled.

"I am very Jewish though - I think we are the most ethical religion in the world.

"It is wonderful to be Jewish, we are smart and bright.

"I was brought up culturally Jewish and I have carried that over to my daughter.

"We go to the temple and we observe the holidays.

"I never make fun of what happened to my husband - if you listen to me talk about it on stage, I am actually making fun of myself."

Being so famous can have its pitfalls, but Joan said she would gladly chat to anyone who comes her way.

"After my husband committed suicide, I had people shout at me in the street in New York that they were praying for me or rooting for me," she said.

"That is great when you are having a bad day.

"I have found that the bigger the celebrity, the nicer they are.

"Perhaps it is because they are more secure in who they are.

"It is the ones who are not as famous who become angry if you don't give them attention."

Joan may be world famous and seems to never stop working, but she enjoys the simple pleasures in life just as much as the next person.

"I do have days off and when I do, I like to sit in bed and do my crosswords or stay at home with my dogs," she added.