Midler is wearing a slinky black dress and a pair of Christian Louboutins. She has aged exceptionally well, like a fine wine; she looks better at 68 than she ever did, her corkscrew curls replaced by an elegant updo. Almost 50 years in showbusiness have taught her a lot: she knows that she must always look immaculate. "Women now, they [have to] pose," she drawls. "They don't want those ugly pictures of themselves on the internet, and I don't blame them. It's like a war! It's poisonous, totally toxic," she says. "If you get on that red carpet, you better be prepared for the results, truly."
She did the Royal Variety Performance this month.
"I met the beautiful Duchess [of Cambridge] and her wonderful, handsome husband and they're lovely, lovely people and I was delighted to be introduced."
One Direction were also there. Did she meet them? "I saw them from across a crowded room," she says, an insincere smile on her face. "Simon Cowell was there, so I didn't dare approach them." She mimes a theatrical retch as she says this.
We are here to talk about her new album, It's The Girls, a compilation of covers of the girl bands of her youth. "The Ronettes, The Chiffons, The Marvelettes, The Crystals ..."
They all had such wonderful names, I say. "Oh yeah, they really did. So evocative. They were completely and utterly wholesome and whimsical. And optimistic. The music was very optimistic and upbeat. The ballads were sometimes sad but you knew things were going to turn out in the end. The music wasn't bleak. This was before Bob Dylan, you know," she says drily.
Midler with the Duchess of Cambridge at the Royal Variety Performance in London this month.
There is only one modern song on the album - Waterfalls by TLC. I ask if she considered using the music of any other contemporary bands. "I couldn't think of a girl group that was modern who had a song as meaningful as [the one by] TLC. I couldn't find one. I mean, who are you talking about? The Spice Girls?" She looks aghast. "I like Destiny's Child. I think that was the last great girl band there was."
We talk about the "pornification" of pop music. "It's terrible! It's always surprising to see someone like Ariana Grande with that silly high voice, a very wholesome voice, slithering around on a couch," - here, she does some slithering herself - "looking so ridiculous. I mean, it's silly beyond belief and I don't know who's telling her to do it. I wish they'd stop. But it's not my business, I'm not her mother. Or her manager. Maybe they tell them that's what you've got to do. Sex sells. Sex has always sold."
But does it sell more now? "Well, whatever strictures there were have fallen apart. And now it's whatever you feel like doing you can do. I mean, apparently people really like to pretend they're having sex. They really like to slap each other's butts."
She slaps her own butt. "I mean, don't ask me. It's beyond me. I'm too old. I don't know what the end game is going to be. I don't know where you go from all that sex in your 20s. I don't know how you sustain it."
If she had any advice for a young woman wanting to break into showbusiness today, it would be this: "Trust your talent. You don't have to make a whore out of yourself to get ahead. You really don't."
Bette Midler may seem as Manhattan as Woody Allen but she was actually born in Hawaii, at the end of World War II.
Her father was a painter who disapproved of her showbiz ambitions. Her mother, a seamstress, named her after Bette Davis and is said to have screamed "Fabulous ... I didn't know she was so witty!" when she first saw her daughter perform.
Midler worked in a pineapple factory before escaping to New York City, where she got a role as one of the sisters in Fiddler on the Roof. She played the eldest daughter.
"She was supposed to be tall and lean," said Midler in an interview a long, long time ago, "and I was short and fat."
But what did it matter how beautiful she was with humour and talent like that?
Midler's sister Judith was killed in a car crash while on the way to see her perform. It is said to have haunted Midler for many years afterwards. But she overcame personal tragedy to achieve professional success. It was in New York that she began singing in a gay bathhouse, with Barry Manilow as her pianist, adopting the alter ego The Divine Miss M. The bathhouse - and what exactly took place there - is the subject of much speculation, but she's always maintained that she didn't notice anything untoward because she was too busy focusing on her own performance. That's Bette for you. Professional to the end.
Musical success (she has won three Grammy awards) was followed by movie success - her first, The Rose (loosely based on the life of singer Janis Joplin), won her a Golden Globe, while her 1988 film Beaches still tops weepy lists.
She has been a brilliant comedienne, too, her mermaid-in-a-wheelchair character ripped off by the likes of Lady Gaga.
"I have dabbled in this, dabbled in that," she says of her varied career. "I'm easily distracted, but focused. Once I decide what I'm going to do, I'm like a dog with a bone. I can't let it go until it's done and it's done well."
But you don't get multitasking entertainers anymore. Nowadays, "the comics don't make music and the musicians don't make comedy, which is so wrong. In the old days, everybody did everything, and that was the best way to do it."
The stage, she says, is her "spiritual home. It's where I live. But I do like being off the stage as well. I have a big life off stage."
There's her husband of almost 30 years, Martin von Haselberg, who gave up his job as a commodities broker to support her career and bring up their daughter, Sophie, now 28. Sophie is an actress who will shortly appear in a new Woody Allen film.
Bette Midler's movie Beaches still tops weepy lists 26 years on.
"My husband and I are both very happy and proud and obsessed."
Then there's her charity, the New York Restoration Project, which has been going for nearly 20 years. Its aim is to plant trees and restore rundown buildings in deprived areas of the city; Midler bought 52 community gardens in the area and is a passionate horticulturist. Her interest started when Sophie was born. She says she looked back to the "sunny" world she grew up in and couldn't bear that her daughter wouldn't get to do the same.
"The whole world has become disposable," she says, concern writ large over her small face.
"People use things once, then they throw it away.
I grew up really frugal. It was the end of the war and people didn't have anything. They had to take care of what they had. They had to polish their shoes.
"I mean, you say polish your shoes to someone nowadays and they don't know what you're talking about!" She throws her hands in the air.
She doesn't allow plastic in her house. All the water bottles in the room are glass. Her work ethos is equally old-school.
"Now you feel entitled to it without working for it. You come out of college and think, 'Well, I can do anything'. No one is willing to learn the game and plunge in before they are a star."
She wishes, if anything, she had been more relaxed about her career.
"I worked a little too hard, I'm afraid. I should have been easier on myself. But I like rehearsal. I love the business."
Will she ever retire?
"Of course I'm going to retire." Oops, sorry for asking. "You just take your time and you just sort of sneak out when no one's looking. I definitely think that will happen."
What's the key to her longevity?
"I think it's ... gee, that's ..." for the first time during our encounter she is lost for words. "I think it's perseverance. Continuing to put one foot in front of the other. And taking advantage of the opportunities. I took advantage of some opportunities that I shouldn't have, but in the long [term], I had more peaks than I had valleys, and I never let anything distress me so much that I couldn't get up off the floor.
"It was a wonderful life," she says, suddenly the narrator of her own life story.
"I did good with it. I didn't shame anybody. I didn't mortify anybody. I didn't take my clothes off. I wasn't caught in flagrante. The fact that they never caught me is really kind of the thrill."
One of her umpteen PRs is now in the room, letting me know our time is up.
"Feel free to make me sound more funny that I actually am!" she says, and I leave with the sense that I have just been in the presence of one of the last great entertainers. A true star.
