Joan Bakewell lives in the most beautiful, tall, moss-coloured, early Victorian town house - bought for £9,000 in 1964, damn her! - in the most delicious north London square. I buzz the buzzer, and she comes to the door. She's as elegant as the house itself, as glossily groomed, and wearing, today, a rather prim navy trouser suit teamed with the most wonderfully saucy, red T-bar shoes. This is the thing about Joan, I guess: formal, earnest, cerebral but giving off these little signals suggesting that, underneath, she might be a bit of a goer. Certainly, Robin Day always took it as read, and used to interrogate her madly at BBC parties: "Do the men you interview fancy you? Do they stare at your legs? At your breasts? Do you sleep with many of them?"
And she was something of a goer. Harold Pinter in the afternoons, and all that. "Thinking man's crumpet", and all that. I ask whether she knows when, and why, "crumpet" came to refer to a sexually delectable woman. "I've never been able to trace it," she says, then adds: "Crumpets are sort of squashy and soak up a lot of butter." Delicious, we agree. I don't say the dimpling always reminds me of cellulite.
I follow her up the stairs to the sitting-room. Her arse is wonderfully neat, I note. I bet it isn't crumpety at all. She is 70. Can you believe it? Can you believe it, Joan? "It is old," she says. "You can't pretend it is late middle age anymore, which is what I did until a few months ago." She looks after herself, goes to the gym. "I don't like getting fat." Dresses with care. She has always adored fashion. "I remember some young producer on Newsnight saying, 'You're so brave, wearing jeans at your age'. I was 48! I couldn't believe it. I still wear jeans. And I'm still into clothes, which is problematic because designers don't give a toss for anyone over 40."
She relies, mostly, on Caroline Charles, the Jean Muir sales - "because I knew Jean" - and the personal shoppers at Fenwick and Selfridges, who, she says, save her the indignity of "going though racks and racks of stringy dresses. The thong." The thong? "The thong sticking out of your trousers. Very strange. Young people will keep on thinking of things grown-ups can't wear, won't they? But if you have a young figure, I suppose they look lovely." Indeed. Does Joan mind being 70? Perhaps, a little. Who doesn't mind getting older? The thought of Joan Bakewell in a thong, though. Is Sir Robin turning in his grave, or doing something else entirely?
Into the high-ceilinged, grown-up sitting- room, with its olive-velvet chairs, expensive music system, book-lined walls, telly. Nowadays, she likes history programmes, mostly. She regrets never having presented a "Starkey-type" programme herself, "as I do have a history degree". Do you ever watch trash? She quite likes Who Wants To Be a Millionaire, she says, and Sex And The City. She adores the clothes, but wonders "why no one ever does any laundry". This is the last series, I say. "And how we will all miss it," she says, with some feeling, but not a toss of her long, luxurious raven hair, because the hair is quite short now, and hennaed a conker-brown.
Actually, now I think of it, was Joan, perhaps, the Charlotte of her day? Anyway, enough of that, because we are here, ostensibly, to discuss her memoirs, The Centre of the Bed, so named because, after two long marriages (first to Michael Bakewell, a BBC head of plays, then to Jack Emery, a theatre director) that both ended in divorce, she can now have the whole bed to herself, no longer has to sleep on her side. "When you get divorced and your partner goes away... widows do it particularly... you sleep on the same side of the bed because you want to fantasise that the other person is still there, but I didn't want to do that."
So you actually physically moved to the middle of the bed? "Oh yes, and it was a really significant thing to do. Of course, it's not really about the bed. It's about being the centre of your own life. Women are taking charge of their lives. They're not just the other half." Sometimes, she can revert, in this way, to Sixties feminist agitprop. Indeed, I am half-feared that, at any moment, she will say: "A woman needs a man like a fish needs a bicycle." But this is totally mean, I know. Her generation of women, the first to properly have careers, the first to properly juggle family and job, were the vanguard, the true pioneers. (At least, that's what Bubbles, my goldfish, said this morning as he pedalled off to work.)
Has she found being single something of a liberating experience? "You can choose the colour of the wallpaper without any consideration but your own taste," she replies. "You don't think: what movie would we both like to go to, because he likes car chases and I like art movies, so what's the one in the middle, the one that neither of us wants to see? It's about having your own way." Any downsides? Things you miss?
A pause. A Pinteresque pause, even. Then: "Having someone to love. Because there is nowhere to put it." This is said with some melancholy. I put it to her that I could be up for adoption, could be settled in this beautiful house - £9,000, damn her! - with Bubbles by this afternoon. Could he chain his bike to the railings, do you think? "I do have friends, children, grandchildren," she replies, hastily.
OK, the book. I'm ashamed to say I rather rushed though the early stuff - aspirational, lower-middle-class upbringing in Stockport, high school for girls, Cambridge, where she ditched the Lancashire accent and met her first husband - to get to the Pinter business. Trouble is, it's not as juicy as hoped. She first met Pinter at a party in 1960, and writes about their meeting as follows: "Harold moved me out of earshot and began to speak. I had heard nothing like it. A torrent of talk - brilliant, intense, witty - the sort of rapturous speech you hear in a play." I am hungry for details. What did he say exactly? How did he look? Did you feel intellectually intimidated in any way? "I just don't remember," she says, primly. I can't look too convinced because she adds: "You can sense that I'm choosing not to revisit it too much. Even though the account in the book is discreet, it was quite hard to write."
I wonder why she wrote it at all. Although her seven-year affair with Pinter was first made public in Michael Billington's biography of him some years ago, she has always frustratingly refused to talk about it herself. Why now? "Because it was, well, my time of life. I wanted to look back. And with Heart of the Matter gone, I wanted an enterprise, something that was moving forward. It is something I've left behind. Indeed, I would have left it behind much more if he hadn't written a play."
The play, Betrayal, based on the whole Joan/Harold/Michael (Bakewell) business. First presented by the National Theatre in 1978, long after the affair was over, Joan can't recall much about the first night. "I could hardly see it, I was a nervous wreck, frozen with embarrassment and apprehension. I can hardly remember how it seemed. I'm only just able to see it now."
Betrayal. The thing about betrayal is that it never ends. It breeds. Joan betrayed Michael with Harold. Harold betrayed his then wife (the actress Vivien Merchant) with Joan. Michael betrayed Joan because, as Joan discovered at the time, he also had a mistress. Joan, once she knew of Michael's affair, betrayed Harold by telling Michael about her and Harold. (The Bakewells decided to continue with their marriage and their lovers. "We were a trim little ship taking a buffeting in the open seas of an exciting life," writes Joan, in her merry, purple way). Michael betrayed Harold, an old friend, because he didn't tell him he knew. Joan didn't tell Harold that Michael knew. Joan didn't...
Hang on, Joan, why didn't you tell Harold that Michael knew? "I was always operating on damage limitation. Not hurting people. We didn't refer, you see, to our families very much. It was a matter of not spoiling something. We didn't think forward and we didn't think back. We just existed at the time. Spoiling something meant it would be different next time, and I didn't want it to be different. It wasn't as though we were envisaging getting divorced and married. That comes into the play but it didn't come into our relationship at all. It was a curiously out-of-time experience."
You just don't seem the betraying kind, Joan, but all the lies you must have told. All the evasions. "I must have just been brazenly cunning." Guilt? "If I felt it, I buried it away. It's hard to remember. I can't have felt enough guilt because if I feel guilty about something I act on it so that I feel less guilt."
Did the children know? (She has two with Michael, now grown up). "They knew when I got divorced from Michael. Because they'd met Harold, you see, and they knew him. But children are incredibly matter-of-fact. They've never been to see the play. Not interested. I dare say they'll skip the chapters in the book. It's not about Mum. It's about this other creature."
Do you see the Joan Bakewell of the Sixties as another creature? "No, no, no, no. I feel it's me." Joan in the Sixties, presenter of Late Night Line Up, with her earnest questions, short skirts, endless legs, long, luxurious, Charlotte-y hair. Over the years, she has complained, on occasion, about too much emphasis on the "crumpet" and not enough on the actual work. But Joan, I say, were you truly a reluctant sex symbol? You could have worn longer skirts. Tossed the hair a little less. Crossed and uncrossed the legs a little less. Tormented poor Robin Day a little less. "I suppose I was keen on being found attractive. I wanted people to find me acceptable. I was grateful they liked me.
"My mother, you see, had always given me a hard time, persuaded me I was unlikeable. She was very critical. She bought all my clothes until I went to Cambridge, and they were very frumpy. I wanted to wear revealing clothes - plunging necklines, as daring as possible. It was defiance. I suppose I had all these sexual hang-ups because she thought it all so wicked."
Joan's mother, Rose. A clever woman at a time when there was no place for clever women, so she became a depressed housewife obsessed by cleanliness and her daughter's virtue. Sex was taboo and "mystification set in early": "Once, on holiday in Wales, when I was 13, I had a physically delicious sensation while galloping a horse along the beach. At the time, I didn't know what to make of it, or for some time to come." Bet you took up horse-riding, though? "We couldn't afford it."
The other thing about Joan, I guess, is that, despite the feminism, a part of her always needed to be defined by men. Will there be someone else? Who knows? But if there is, I hope she not only keeps resolutely to the centre of the bed, but appropriates most of the duvet, too. After all, as Bubbles once so wisely pointed out: "You can have it all, if you hang on fiercely enough and aren't afraid to use your elbows." And then he was off, pedalling like mad, as he was rather late for work that day.
'The Centre of the Bed' is published by Hodder & Stoughton, £20