Sandi Toksvig knows how to be charming.

Her latest book, a guide to modern manners, provides tips on handling every common social situation with grace and aplomb. It covers the full spectrum of appropriate behaviour, from where to lay the napkin on a formal place setting to how to conduct yourself on public transport, and all in a tone that is encouraging rather than hectoring.

Even so, the prospect of having lunch with the woman herself in a London restaurant prompts something like pre-exam jitters.

I run through the rules in my head en route to the Clerkenwell bistro, feeling a little flustered. Don't put your elbows on the table. Don't play with your hair. Remember to break off little bits of bread roll and butter them individually before eating them (makes less mess, apparently). Got all that. Ah, but what about shaking hands? Should I shake Toksvig's hand? Oh dear, the rules aren't clear. Didn't she say something about shaking hands being a predominantly male to male activity?

Too late, I'm here, she's arrived, we're introduced, no handshake? OK, no handshake. Looking dapper in crisp shirt and blazer, she inquires politely about my train journey down. I explain it was very comfortable, thank you, and add as a joke that there was hardly anyone picking their nose. She looks a little startled at this but quickly recovers herself and tells me she's so glad. Oh dear, that was too much; an etiquette faux pas in the first minute - what was it she wrote about avoiding off-colour jokes? This doesn't bode well for the bread roll.

Fortunately, Toksvig has one simple rule which encapsulates all the others like an etiquette great commandment: think about other people more than you think about yourself. Whether because of this or simply because Toksvig is such a well-informed and interesting companion, lunch turns out to be a very easy-going affair.

This is in spite of the fact that, for her, today's arrangement is somewhat uncomfortable. She has agreed to have her photograph taken in situ, but this inevitably means creating a bit of a stir in our corner of the restaurant, drawing the attention of fellow diners, which clearly jars with Toksvig's notions about good manners. It helps that the pictures are taken by her civil partner Debbie, a photographer turned psychotherapist, but once the deed is done, and Toksvig is seated with her back to the restaurant, she visibly relaxes.

A writer and broadcaster, Toksvig, 55, divides her time between writing books and drama on the one hand, and presenting and performing on the other. Her unfailing civility, notwithstanding the odd risque joke on The News Quiz, is her trademark and has helped make her something of a national treasure.

Toksvig admits she has been hot on the subject of manners for years. Her own pet hates are drivers who fail to indicate and men who take their shirts off in public. ("There's an awful lot of lard out there. No woman would do that.") She has been tough on manners with her own children (Jessica, 25, Megan, 23, and Theo, 19) all their lives. "It's mainly because I wanted to send them out in the world and have everybody like them," she explains.

It quickly becomes apparent, however, that beneath Toksvig's support for thank-you notes and opening doors for others, there is a broader yearning, for more kindness and consideration in human interactions.

Much of her own behaviour is informed by her rather unusual childhood. Toksvig describes her late father, Claus, as "the most charming man I ever met". (Toksvig's British mother Julie Anne, now in her eighties and living in Surrey, is a "force of nature", she says, and they talk almost every day.) The Danish Broadcasting Corporation's first foreign correspondent, Claus Toksvig was posted from 1967 to 1974 to New York (where Toksvig went to school) and then London. He was famous - the most famous man in Denmark, she says - and he had "the most impeccable manners". "Whoever he was speaking to, they had his attention."

She recalls one occasion when, aged 11, she tried to tell him during a business meeting at a restaurant that the wine he had ordered was corked (she had been allowed a little, with water). After shushing her twice, Claus realised she was right and, in front of all his guests, apologised for having ignored her. Toksvig hurriedly adds that yes, she realises it is "weird" at 11 to know that wine is corked, but the point is that she remembers the incident because she was treated with such respect.

After moving to the United States with her family, she acquired a New York accent, but lost that after being sent to an English boarding school aged 14, which she hated. "It was one of those bits of your life that I'm sure makes you stronger, but it made me very determined that when I had kids they were never going to go away," she says, resolutely. "You didn't get any hugs. No matter how old they are, children need cuddles."

Later, at Cambridge, Toksvig joined the Footlights as a contemporary of Stephen Fry, Hugh Laurie and Emma Thompson, and after graduating, she became one of the Comedy Store Players and went into television, presenting children's programmes including No 73. She is remembered by child fans as a cheerful, sunny character, but when she talks about how she was treated as a woman in comedy 30 years ago, it is with contempt. "I can't remember the number of times I was told, 'Don't you worry about that, you pretty little thing.' Wow. I've got a first-class degree from Cambridge, but OK."

That era (the 1980s) is now under the spotlight, in the wake of the Jimmy Savile scandal. Toksvig spoke last year about having been groped by a "famous individual" on air during that period, though she declined to reveal his identity. How did colleagues react when she told them at the time? "They laughed," she says indignantly. "They would often tease you that you weren't good-looking enough to be groped. Or how lucky you were, because it was a very famous person." She insists, though, that she did not bring up the case to have a go at the BBC; far from it. "Put it in its cultural context and it happened all the time to every woman in every line of work. I'm really sorry that the BBC got maligned in this way because they simply were not responsible, it was society."

Petite at 4ft 11in, she has a quiet, soft voice and attentive manner, checking on my water glass and inquiring if I'm enjoying my food. She gives the impression of craving anonymity, commenting rather wearily that, as a child, she and her family were photographed everywhere they went. She adds: "I'm not interested in fame or in courting publicity or any of those things." She has a Twitter account but only to prevent impersonators; she never tweets, and mentions with incredulity the fact that a stranger on a train once tweeted a photograph of her eating a sandwich.

Well-turned anecdotes pepper our conversation, but behind the humour there is a certain watchfulness.

This is hardly surprising, given the hostility that has come her way over the years, particularly over her sexuality. She and her former partner Peta Stewart had their three children by artificial insemination, fathered by a friend. When she learned that a newspaper was going to out her, Toksvig came out in a rival title. When the story emerged, she received death threats and the family was forced to go into hiding for a spell.

In the 20 years since, there has been much change in the rights of lesbian, gay, bisexual and transgender people, and in their visibility in the media. Toksvig comments that she loves that her children's generation have friends who are gay and think nothing of it.

Still, a chapter in her book is devoted to middle-aged people who don't know how to behave when they meet a gay person. There were experiences she had growing up that she didn't appreciate, she says, and as a consequence, wants to steer others away from such clangers. "I don't want anybody to say to me, 'I'm fine with it, I accept you.' You think, wow, thanks so much, because if you hadn't I would have killed myself."

A regular on panel shows such as Whose Line Is It Anyway? and QI, Toksvig has written more than 20 fiction and non-fiction books, as well as plays, but is currently best known as the presenter of Radio Four's The News Quiz. She was asked to take on the role by phone one evening while parking her car, said yes without thinking and has now been at it for seven years. She enjoys it, though says she cannot do it for ever.

Toksvig quotes a maxim of her father's, that no journalist should write that which he cannot say as a gentleman. She thoroughly approves, but how does that fit in with biting political satire? "I make jokes about politicians and that's my job, but I try to make sure it's based on fact," she says. "I try to make sure we don't tell lies."

Inevitably, her role lampooning the political classes hasn't endeared her to everyone. Some critics of the BBC believe that the treatment of Conservative ministers on The News Quiz amounts to left-wing bias at the corporation, though long-time listeners who recall the savaging of Nick Clegg and Gordon Brown, would probably disagree.

Still, Toksvig found herself the subject of a columnist's tirade in the Daily Mail earlier this year, after she had commented on Hilary Mantel's remarks about the Duchess of Cambridge. The Mail labelled her "Toxic Toksvig". Asked if she was surprised by the strength of the invective, Toksvig becomes exasperated.

"What I actually said was that I think the Duchess of Cambridge is probably one of the most charming people you could hope to meet; she's certainly extremely beautiful and I have no axe to grind with her whatsoever.

"What saddens me is that she is one of the greatest role models for young women in this country and she achieved her position through marriage, she didn't achieve her position through skill, talent. And I added on to that, 'So she may be charming but I don't know a single opinion that she holds and it's all very Jane Austen,' meaning no disrespect to her whatsoever, meaning that it's an odd world where the single most important female role model is one who is a Mrs Somebody.

"It's not offensive."

She feels that her quotes were being taken out of context and presented in a way that didn't make sense. "Jane Austen's women have very strong opinions," she points out.

The memory clearly rankles. The Mail article accused her of being "spiteful" and "unfunny".

All of this clearly saddens the presenter, who feels depressed about newspaper stories that "flirt with the facts". We are back once again to kindness and consideration.

It may help to explain why, when she thinks about the future, it is a future where she is no longer in the celebrity limelight. Toksvig has a house in Denmark - a wooden cottage in the woods by a lake "like a Bergman film" with no mobile signal - and goes once or twice a year to relax, away from it all. Study, travel, spending a year in Copenhagen, going somewhere where she is more anonymous: these are all on the to-do list.

"I suspect what will happen at some point is that I will give up what I call showing off and perhaps work for a charity as their spokesperson or do some civic role, something where I feel I could maybe bring some benefit." She will always write, she says, and has a play in mind set in an old people's home. "But other than that," she concludes, "I'd like to go home and make soup." n

Peas & Queues: The Minefield Of Modern Manners by Sandi Toksvig is published by Profile Books, priced £12.99.