Instead of horns, this she-devil has curlers jutting from her hair. And it is not sulphur she trails in her languorous wake but nutmeggy fumes of baking pie (to borrow a phrase from the playfully camp introduction to her bestselling cookery book How To Be a Domestic Goddess). Where a devilish tail might be, there’s a microphone wire. It runs up her back and emerges from the collar of her pale green silk pyjamas. She is wearing these because she’s filming a scene in which she raids her fridge for a midnight snack. Are silk pyjamas what she really sleeps in? ‘No,’ she says crisply, raising one eyebrow. ‘I don’t wear anything in bed. But I’m not ready for a nude scene quite yet.’

There is a frivolous atmosphere: banter among the film crew, mobile phones ringing, the clattering of utensils. Rubber matting has been laid down to protect the floor and, with lights, cameras, cables and monitors cluttering up the place, you can see why Nigella compares the experience to ‘having the builders in’. She removes a tray from her oven, the director says ‘cut’ and a make-up artist rushes over to even out the skin tones on her manicured hands, in case there are any red marks left by the hot tray. There are a couple of retakes to do before it’s a wrap – and the director asks the presenter if she thinks she should be ‘matronly or camp’ for a scene in which she sprinkles pomegranate seeds with her fingers. She opts for sultry: ‘Mmm. Just look at these beads pouring down like pink rain.’ Nigella’s children – Cosima, seven, and Bruno, four – run in wearing school uniforms, sucking lollies. Their nanny, an Italian, follows. Two Birman cats slink in after her. It’s a chaotic scene. Nigella likes it this way. It distracts her.

That evening, upstairs in a white room lined with oil paintings and vases of purple tulips and blue nigellas, the mood is different. Nigella is sitting on a sofa, talking about her husband John Diamond, the journalist who died from oral cancer in March. She is now wearing a black skirt and clingy V-neck top and has poured a couple of glasses of champagne (Taittinger, her favourite; she drinks it most nights because it doesn’t give her a headache or acid stomach). Today she has been filming the fifth in a series of ten episodes of Nigella Bites. Her husband died while an earlier episode was being filmed. ‘I took a fortnight off. But I’m not a great believer in breaks.’ She says this briskly, neutrally. ‘I don’t want to be rattling around inside my own head. I did feel I was spiralling into a Kathy Burke character and tried going out, but I prefer it here. Filming keeps me busy. It absorbs me.’

She sips from her glass. ‘Of course it is displacing certain thoughts but, in a way, I don’t think grieving should be your full-time job. That seems a rather modern idea. To act as if you don’t have a life is probably not sensible, especially when you have children. Also, I have to say, I found it very constraining having to look demure under my veil, metaphorically speaking. I can’t be other people’s perceptions of me. I can’t act out other people’s feelings for me. I find it very intrusive.’

The response to John Diamond’s death was extraordinary. Most broadsheets devoted several pages to it. Even the Prime Minister paid tribute. Was Nigella taken aback by the public sympathy? ‘To tell the truth, I wasn’t at that stage very focused on it. But I have put all the clippings in what I call my Morbidobox, and I haven’t read them all yet. I was pleased because I hadn’t foreseen any of it, in the sense that I didn’t know John was going to die when he did.’ She was, she adds, amused by a Private Eye cartoon which showed a graph of the amounts of newspaper space devoted to the deaths respectively of an artist, a scientist and a journalist – naturally, the journalist wins by a long way. ‘John would have found that funny. He was always for being public. I was married to someone who liked all that. I never did. It wouldn’t be my way of doing it. I gave into it.’

John Diamond, of course, found it therapeutic to write about his illness in his column for The Times and in his best-selling book C: Because Cowards Get Cancer Too. He was witty and thought-provoking on the subject and, with cruel irony, it was the making of his career, bringing him the fame he had always wanted and, as far as some of his readers were concerned, turning him into a secular saint. But his levity in print, it seems, was sometimes counter-balanced by his anger, depression and suicidal urges at home. ‘You can do an awful lot of that [being droll] in 800 words a week,’ Nigella reflects. ‘But doing it in your life is another matter. Real life does have a way of asserting itself. Has to. Of course. It was difficult because I had to go on a programme once to defend him, which I did willingly, though in many ways I agreed with his detractors. It was a difficult position. It wasn’t a matter of [him] being dishonest but of giving a truthful account which was inaccurate. Anyway, you don’t have an obligation to tell all. Right now, I have every desire to be completely honest and truthful; I’ve got absolutely no desire to tell you the whole truth.’

John Diamond was beginning to establish himself as a broadcaster when he was diagnosed with oral cancer in 1995. Clearly he felt proud of Nigella when the first series of Nigella Bites became a hit last autumn (even Victor Lewis-Smith, the London Evening Standard’s notoriously acerbic television critic, felt moved to call her ‘formidably charismatic’), but does she think her husband also felt a little jealous? ‘Not really, because we were very different sorts of journalists [the couple met in 1989 when they both worked on The Sunday Times, she as the deputy literary editor, he as a travel writer. They married in 1992 and then both had columns in the Saturday Times Magazine, Diamond on dying, Lawson on lipstick]. But obviously the situation was complicated. On the one hand, he had too great a desire for me to do more than I might have wanted, and, on the other hand, there was envy. But of all the problems that were thrown up in the past two years, I would say that that was the least significant. Work is work. John, had you asked him, might have said differently. I don’t know.’

Because he could not speak – having had his tongue removed in an operation in 1998 – John Diamond communicated in company by writing with an ink pen on notepads. One of his last messages to his wife, written in his final hours, read: ‘How proud I am of you and what you have become. The great thing about us is that we have made us who we are.’ Did he mean they had reinvented themselves? ‘Often two people who are quite different get married,’ Nigella says, ‘and you think you like someone because there is that difference. But actually – and this may sound like gobbledegook – what you are attracted to in the supposed difference is the chance it will give you to accept a part of yourself you didn’t know you had, or you secretly knew you had but were embarrassed about. So for me that meant John’s showy-offy character. Because I’m naturally shy. Over the years I probably took on a lot of that character, especially when I took on John’s voice [he would talk as best he could and she would interpret for others]. It turned me from being a quiet person to a constantly talking person. In the same way, he thought of himself as funny, and I was the serious one, and yet over the years he became more relaxed about not having to crack a joke every five minutes. In that sense, over time, you take on each other’s characteristics and the differences evaporate.’

In other ways, I suggest, they remained opposites: whereas he seemed to reject the need for privacy and wanted to externalise everything, she preferred to internalise things and keep her own counsel. ‘Sort of, though I have very good girlfriends I talk to. Yes, John was very open and honest but also self-deluding. Necessarily so. I try to be open. I’m not good at being by myself. I think John got it right in that he was gregarious but also liked his own company. Whereas I don’t like going out and I don’t like my own company!’ She feels lonely? ‘Bored, anxious and lonely.’

On a superficial level, Nigella’s claim to shyness is baffling. She has a ready wit, as she demonstrated on Have I Got News for You last year. Her intelligence, bookishness and confidence in public are obvious (she read modern languages at Oxford, has been a Booker Prize judge, and on programmes such as Question Time comes across as being articulate and thoughtful). And, as if these qualities weren’t enough to bolster her ego, she was named Author of the Year at the British Book Awards a few months ago, as well as ‘the third most beautiful women in the world’ in a recent survey (she comes in after Catherine Zeta-Jones and one of the Corrs).

‘I was shy as a child,’ she explains patiently. ‘Now I’m not really shy any more, unless I’m with shy people. I find it contagious and I don’t know what to say. But I don’t think shyness is something one should feel apologetic about. When you are younger it seems an appropriate way to respond to the world. I think it was to do with my unhappiness and lack of confidence. But even now I wouldn’t want a life where I was always going out to big events. I tend to see the same six people all the time.’ She flicks her long black hair back over her shoulder. ‘I’m someone who either has warm and intimate feelings for someone or I’m not interested in them at all. I don’t have an in-between.’

Does she think strangers feel awkward with her because they are intimidated by her looks? She laughs. ‘That’s like a “when did you stop beating your wife?” question. I’ll tell you what it is: women are only intimidated by thinness and one of the reasons women like me is that I’m not thin. I promise that’s true. It’s not just a facetious answer.’ Her weight fluctuates, she says. ‘I’m on the up at the moment. I am greedy. I eat under stress. When you are eating, the rest of the world is tuned out. And when you tune back in you feel guilty about having been greedy and the rest of the world is still there, so you have to carry on eating!’

Dominic Cyriax, the director of the new series of Nigella Bites, initiated a weekly weigh-in for the crew and Nigella feels obliged to enter into the spirit of the thing. ‘There is a competition between me and the soundman for who is putting on most weight. I’ve put on 6lb since we started filming. Food is a narcotic. Like being at the breast. I do mind putting on this weight because you feel quite vulnerable with a camera pointing at you. But when I am thin my face looks too thin!’ She shakes her head. ‘I despise myself for worrying about it sometimes because in the scheme of things it is very shallow.’

Nigella is self-deprecating – she says she doesn’t have a muscle in her body – but is this, like false modesty, a form of vanity? ‘I’m vain in the bad ways but not the good ways,’ she says. ‘I worry about what I look like but I’m too much of a slattern to do anything about it. I will feel guilty because I ate all the children’s Maltesers. I go around in trainers and horrible clothes without make-up and without brushing my hair. I’m lazy.’

With a rueful smile, she concedes that she might have to start making more of an effort. Two weeks after John Diamond died, the Mail on Sunday ran a carefully insinuating story about Nigella’s friendship with the art collector and advertising mogul Charles Saatchi, suggesting that the two had become ‘very close’. A paparazzo’s snatched photograph was bought by the paper for more than £20,000, as if to justify the story. ‘We were leaving a restaurant for God’s sake! At lunch-time. With me in no make-up and glasses!’ Was she miffed? ‘Not really. One of the things about when you go through a lot is that you don’t have it in you to feel. . .’ Pause. ‘I didn’t have the energy to mind a lot. But I did feel that to have a photograph taken of yourself and not know about it is quite horrible.’

She doesn’t like having her photograph taken (even when she likes the results). ‘Although filming is tedious, at least you are doing something. I’m not an inactive person. I don’t like the passivity of posing for photographs. It’s so boring I want to punch someone. It’s like going to the dentist’s: it’s not the pain I mind, just the sense I’m being held captive. I like doing programmes like Question Time because they don’t allow you time to observe yourself. You are too busy thinking of an answer. Even though I like to think of myself as a docile creature, I probably inherited the Lawson gene of combativeness.’

If women like her because she’s not thin, presumably men like her because she is coquettish on camera – the enigmatic smile, the arched eyebrow, taking a fraction too long over licking those sticky fingers of hers. ‘You call it being coquettish. I call it simpering. And, yes, I do sometimes worry I’m overdoing it. Television magnifies aspects of my character. I am quite flirtatious. Regardless of sex or species.’ A short laugh. ‘I do it as an act of courtesy rather than an encouragement to anything sexual.’

Although she once said she was neurotic enough to see the negative in anything positive – ‘It’s a great Jewish gift’ – she tells me she doesn’t worry about the inflammatory effect she has on lonely men – and potential stalkers – sitting watching her on their televisions at home. She’s not a worrier, she adds. Indeed she rarely bothers to lock her car. If it gets broken into, it gets broken into. This sense of perspective is understandable. Having lost her mother, sister and husband to cancer, she knows worse things can and do happen in life. (Her mother Vanessa died of liver cancer at the age of 48, when Nigella was aged 25; her sister Thomasina, who was 16 months younger than her, died from breast cancer at the age of 32.) ‘I’ve learnt not to dwell on the future. I suppose I do think that awful things can happen at any moment, so while they are not happening you may as well be pleased. Having children around you makes you want to live in the present. You have to make things as normal as possible.’

In terms of bringing up her own children, what lessons did she learn from having a famous father, Lord Lawson of Blaby, the former Chancellor of the Exchequer? ‘Politics is very different [to television]. The wonderful thing about having a famous father is that he knew famous people and so you grow up having no reverence for fame, which is very healthy. You know it doesn’t mean anything.’

No doubt there can be a shy, reserved side to Nigella Lawson – and some people interpret this as coldness – but it is not in evidence today. She seems flamboyant, if anything, and perhaps this is a persona she can slip in and out of (John Diamond once described her as ‘a gay man trapped in a woman’s body’). Sitting sideways on the sofa, her Paul Gascoigne legs (her description) tucked underneath her, she is relaxed, warm and likeable – which is a relief, quite frankly, because her brother, Dominic, is the editor of The Sunday Telegraph and he has, she tells me, a tendency to feel overprotective towards her.

Nigel Lawson must have had high expectations of a daughter he named Nigella. And he set high educational standards for his children (Nigella went to Godolphin and Latymer in London). Does she think the knowledge that her father was a high-profile politician gave her an edge in life? ‘I don’t think of myself as the daughter of a former Chancellor. I think of myself as myself.’ She won’t be cajoled into expanding on the subject. When How To Be a Domestic Goddess was published last year, Nigella was accused of being part of a post-feminist movement which glamorises domesticity in an attempt to manipulate the working woman into feelings of guilt. Newspapers devoted leader columns to the issue and two columnists had a spat over Nigella in print: Carol Sarler acting for the defence in the Observer, and Charlotte Raven for the prosecution in the Guardian.

‘I don’t take criticisms personally,’ Nigella says, ‘which must be very annoying for people who mean them personally.’ Smile. ‘Some people did take the domestic goddess title literally rather than ironically. It was about the pleasures of feeling like one rather than actually being one. I had to take the view that the people who were saying these things were being deliberately obtuse to make good copy. I do regard myself as a feminist. I was never suggesting that women shouldn’t have a job, just that they could enjoy cooking when they put their briefcase down on a Saturday morning. Just because I want to make a cake it doesn’t mean I will vote how my husband tells me. Anyway, the idea of me being a domestic goddess is such a joke. Luckily I had plenty of negative character witnesses; my husband said my bedroom looked like a jumble sale. He was very amused by the idea that I was in any way domestically adept.’

Private Eye ran another cartoon last autumn which showed a man reading his newspaper, every section and supplement of which had a Nigella story. Does she worry about being overexposed? ‘Yes. Sometimes it can feel preposterous. I thought, “I’m getting bored of it, what will other people feel?” So then I thought I wouldn’t do any more [publicity] until the new series. I enjoyed most of it though. There was a local paper which had a caption saying, “Nigella” – they never use my surname – “every thinking man’s fantasy and every thinking woman’s nightmare.”‘

She laughs. ‘I thought that was rather brilliant! Might have to frame that.’ Cosima comes downstairs in her nightie. She can’t sleep. Nigella takes her back to bed and, when she returns, I ask how she sleeps. ‘With sleeping pills.’ Does she have any recurring dreams? ‘No.’ I nod towards a book about Freud lying on a window ledge. ‘That? One of the crew took it off the shelves.’ Has she considered being psychoanalysed? ‘I’m a great believer in it. I’m interested in why people behave in certain ways. Dominic says I’m the last Freudian.’

In the 1998 television documentary Tongue Tied, about her life with John Diamond, she said she couldn’t read when her husband was in hospital, so she turned to cooking as a form of escape instead. It was the same when her sister was dying, only then she took up embroidery. She also said that she couldn’t write her best-selling book How To Eat until long after her sister and mother had died because cooking had been a pleasure she shared with them, and the thought of writing it would have made her too unhappy. She was only able to write it when she realised that food is the opposite of death. ‘It’s about keeping yourself alive.’

Julie Burchill took up this theme in her Guardian column recently: ‘The reason why many women remain uncomfortable about the Nigella Lawson phenomenon is not that (just) we are green-eyed bitches jealous of her biblical beauty, but because the whole Domestic Goddess shtick would never even have occurred to any contemporary women who hadn’t suffered such a sadly disrupted life. Of course Nigella wanted to play house on such a grand scale – it was probably the only thing keeping her sane. But I find it as uncomfortable to watch as I would a stranger acting out an extreme sex fantasy. It’s just too raw and personal.’

Does Nigella find it galling when strangers try to psychoanalyse her? ‘There was an element of the comfort-cooking theory that was accurate because if you like feeding people and you are living with someone who can’t feed, inevitably you will put more energy into it. But it is grossly distorted. Textbook stuff. Please. It’s very simplistic isn’t it? Clumsily done. This view that I cook to fill a void in my awful, empty life. . . Actually, I cook because I enjoy it and because I have small children and it helps to have a job I can do at home.’

It is obvious what people mean when they say Nigella is charismatic, but there is also something remote and inscrutable about her. Clearly she is ambitious, but what motivates her? Not money especially (she recently turned down a lucrative offer to appear in Sainsbury’s advertisements); nor fame (‘I don’t think I give off that neediness for an audience.’) A recurring theme of our conversation is that she fears boredom; perhaps that is it. She thinks her interest in cooking is about to wane because she has ‘a moving-on temperament’. She couldn’t move to the country, though, as her brother has done, because ‘I would panic there. I don’t mind the landscape, it’s the country village I loathe. I get bored. The country is like Christmas: nothing to do but eat and drink.’ Writing a column about herself ‘would bore me and embarrass me’.

Nigella inhabits a strange world of extremes: she has experienced extreme tragedy, extreme success (at the moment there is a bidding war for her programme in the United States) and has the advantage of extreme beauty. Yet her friends remark upon her self-possession, as well as her ability to glide through life. She takes normality, or her version of it, wherever she can find it. According to one of her friends, Olivia Lichtenstein, the idea of Nigella as an ice maiden is laughable because, when you get to know her, she is kind, gentle and honest. She doesn’t take herself too seriously and, says Olivia, though she misses John terribly, is not a sentimental person.

What of Nigella’s own sense of mortality? Did turning 40 trouble her? ‘I don’t have a big thing about getting older. My sister was 32 when she died. It would be an obscenity to mind about being 40. I would rather not have any – what are they called in advertisements? – visible signs of ageing. But it doesn’t give me panic attacks. I don’t think I’ll be weeping over old pictures of myself as I grow older. I feel I live off my wits.’ She laughs. ‘You may feel differently. My looks don’t absorb me as much as everyone says. But then, I’ve had other things to preoccupy me lately. I would be a rather strange person if I was sitting around striking poses, reading my cuttings. Don’t you think?’