The Wealthy Greek's Contract Wife. The Prince's Chambermaid. The Italian Billionaire's Secretary Mistress. Mentioning the titles of Penny Jordan and Sharon Kendrick's latest novels for Mills & Boon draws embarrassed chuckles from both of them.

"Titles are contentious, I tell you," says Kendrick. "[Mills & Boon] want the title to reflect exactly what's in the book" – the subtext being that the authors might prefer something a little more subtle. "I never bother about the title," agrees Jordan. "When I buy books I buy by author. But Harlequin must know how to run their business."

In Kendrick's and Jordan's cases, they clearly do. Jordan is the acknowledged queen of Mills & Boon. She's been writing for the publisher since 1981, has produced more than 170 novels and sold more than 70m books around the world. Kendrick, meanwhile, has just delivered her 75th book. That's 75 heroes, 75 heroines, 75 all-consuming love affairs and an estimated 150 sweaty sex scenes – Mills & Boon couples usually do it at least twice in the course of their 55,000-word romances. How, exactly, do these authors keep it up?

"It is very difficult to have a new take on an old story, and romance is an old story – it's been there forever. It has to ring true to the reader but at the same time you have to write in a way that keeps them turning pages," says Jordan, who churns out 5,000 words a day, writing four Mills & Boon novels a year, as well as two sagas for HarperCollins as Annie Groves. "You know you've got to grab their attention by the end of the first page." In fact, in her romance A Bride for His Majesty's Pleasure, the scene is set by the end of the first paragraph: "'And if I refuse to marry you?' Although she did her best not to allow her feelings to show, she was conscious of the fact that her voice trembled slightly. Max looked at her. 'I think you know the answer to your own question.'" The reader knows what they'll be getting – ruthless ruler, virgin bride – right from the start.

Jordan always begins, she says, with the issue the characters have to overcome in order to be together. "Romance is romance. For me a lot of the fun of writing comes from the problems I give the characters. They have to deal with them in order to feel confident with the relationships they have," she says. "I start with the central conflict, with the problem, then I build characters who will enable the problem to work from the readers' point of view. In the book I've just finished, neither the hero nor the heroine want commitment. He's a bit of a playboy, she's quite withdrawn. It goes back to them both feeling abandoned by their parents."

Maisey Yates, who landed her first contract with Mills & Boon in December, agrees. A "stay-at-home mom" in southern Oregon, Yates produces around 2,000 words a day. At the beginning, she went out to write in a coffee shop when her husband came home, but now she knows what she's doing, she'll write at home with the kids. Five books a year, she thinks, "is doable for me". "Usually I'll get a vague idea of a conflict, then I'll start to think of a character," she says. "Once I've got my first character, and it can be the hero or the heroine, I try to figure out their issues. Then I think about who could come along and mess things up." In The Virgin Acquisition, which will be published in August, Yates's heroine is trying to win back her father's company from the hero. In another of her novels, yet to be published, a career woman who wants to be a mother goes to a sperm bank, and mistakenly ends up with the hero's sperm – it was meant to be a sample for his wife, but she's passed away.

Kendrick, who writes four romances a year, admits to getting ideas "all over the place", even through reading the Daily Mail. "Let's be honest: you have to have some kind of vehicle, and that's the real challenge. Everyone knows the hero and heroine are going to end up married so really the only reason to read them, like all good books, is a compelling story." She insists that, in order to write with integrity, "You have to believe." If people approach them cynically, or try to write tongue-in-cheek, it doesn't work.

She explodes the myth that Mills & Boon writers are provided with templates for their stories. "The structured plan is rubbish. We are allowed as much artistic freedom as will work," she says. "Obviously there are things that work and don't work. The plotline where the hero is trying to build a factory and the heroine is trying to save a rare toad is not a very sexy premise. And you wouldn't want a short fat balding hero – women know too many men like that. Mills & Boon is about escapism and fantasy. It drives me mad when people say 'don't you think you're deceiving women?' I don't think we're completely thick." Although Jordan is clear that she doesn't "get given a tip sheet" for her books, she acknowledges that "every genre has its own little rules". "They're not written down, but if you diverge from reader expectations they won't read your second book," she says.

Once the conflict is in place, the writers look to identify their heroine. While Kendrick admits that "It doesn't matter how you describe her, you'll always have a dead-ringer for Angelina Jolie minus the tattoos on the front cover," her heroines, she says, "are not always beautiful, and like most women are plagued by insecurities. I'm not very good at writing high-powered career women. It could be because I haven't had a high-powered career myself. But if she's a barrister or a newspaper editor, it wouldn't really be feasible – I want her to be spending time with the hero. She tends to have to be flexible. And if she's a chambermaid, if she's sacked it's not the end of the world."

Jordan isn't so sure. "I'm always interested in giving them interesting careers", she says. "There was a fad for Cinderella-type heroines. I've tried them, but it doesn't fit me so well. I have had them with money problems, but with careers prior to money problems. I want them to assert themselves when necessary." Yates agrees, saying she likes to go for "feisty career women". However, Jordan, who's been writing romances for 33 years, usually makes her heroine either a virgin, or inexperienced. "I think of it as a shorthand for me," she says. "It's always by choice. When my heroine meets the hero, she wants to go to bed with him. For the reader, that's the mark of the effect he has on her. Because you've only got so many pages, it would be very difficult for me to create a heroine who's had lots of partners and immediately knew there was something different about this one."

Then comes the hero. Sheikhs are popular, Jordan and Kendrick say, as are Italian billionaires, Greek tycoons and princes. The sheikh, Kendrick says, "represents the ultimate female fantasy – dark, autocratic, completely powerful, outrageously chauvinistic". However, she says, "he often isn't predatory, as he doesn't need to be. In the 70s and 80s the Mills & Boon hero was putting it about, then with the advent of Aids we had to make slowly sliding on a condom part of the love play."

For Jordan, the hero also has to have a charitable side. "He's obviously got to be sexy and high powered because they go together. And they always like them to be well off. But for me he has to have some interest in charity, to do something for the good," she says. "Often when my heroines discover that, their animosity is melted. I don't like a hero without a softer side. He's often damaged by something that's happened in his life, often to do with money. He will be more outrageous to the heroine, and harder on her. He realises he is beginning to feel, he has to resolve that conflict."

And Yates, who at 23 is the publisher's youngest author, says she likes "to play with the conventions a bit. He's still an alpha male, but he's maybe a little more willing to talk about things at times". Her characters are usually pure imagination, but sometimes, she says, she'll "grab a picture, usually of a model, not someone well known" as a template. "I'm really picky about my heroes though, they're a little more perfect in my head," she adds. Kendrick doesn't "do the picture thing. Others put up pictures of actors or models with awful overdeveloped six packs. [But] imagination is much better."

Once the two central players, and their issues, are in place, then, of course, comes the sex. "It is very, very difficult to write about sex," admits Jordan. "You think, did I say that before? I don't have a set of actions, one to five, but there are only so many variations. I try to make it unique for each set of characters, but obviously I must go over the same territory. Straight sex is straight sex. It's more really trying to capture the emotional intensity."

Over the years, Jordan says, more sex has crept into her books. "There is more now, and it's more detailed," she admits. "But I've always wanted my heroines to enjoy sex. Perhaps in the earlier books they were more reluctant to admit they enjoyed it. Now it's a battle within them – they're enjoying sex with someone they might be falling in love with, but they don't like." She never, she adds, writes abusive sex.

Kendrick insists that, no matter how many times you've written one, it's important not to be blasé about sex scenes. "That might imply I'm complacent and that does not make a good bedfellow," she says. "Some writers will go through and leave gaps. I won't do that. It's all the flow of the story. I have to write sex knowing how they're feeling. I have to be her, and imagine him – by that time I will be in love with the hero so it's not that difficult to write." It's a similar process for Yates. "Maybe I was embarrassed afterwards, reading them, but at the time, because I'd spent so long building up all the tension, those scenes came the fastest."

All three authors are adamant that this is a great way to make a living – although Jordan is a little shocked to discover she's written quite so many. "Have I? I probably have. I've been writing since just after my 30th birthday and I'm 63 now. Should somebody my age still be writing romances? Am I still on trend with things? I don't know. I still love writing them. It's the readers' decision," she says with rather touching concern – the readers are still buying her books in their thousands. "The best way," she muses, "to describe the difference between now and then is to say, in the words of Mrs Patrick Campbell, that it's like 'the deep, deep peace of the double bed after the hurly-burly of the chaise longue'."

What Jordan loved – what she still loves – when writing, is "learning about the character, what prevents them from reaching happiness. There comes a point when the character becomes real. It still delights me," she says. "At the end of the day everything I write is about relationships. I'm never going to be a great big famous writer because I don't write great big famous-making scenes, more the nitty gritty of everyday life. And that's what I really enjoy."