Naturally I have to read Cecelia Ahern’s chick-lit novel before I interview her. Still, chick-lit, lots of sex and shopping, right? I plough through all 424 pages, in vain. Sporadic shopping, no sex.

How, I demand of the taoiseach’s youngest daughter, can you write bestselling chick-lit without sex?

“I didn’t think at any point in the story that it could come into it. It wasn’t important,” says the 22-year-old. “Holly certainly wasn’t ready for that.”

The lead character of PS, I Love You is indeed a grieving widow whose husband leaves a series of letters to help her cope with grief and life. But Holly’s friends get drunk, married and pregnant. Couldn’t they, well, you know?

“I wouldn’t go into a sex scene with her friends, because it’s not about them,” she says. “I probably wouldn’t be comfortable with that, to be honest. Even when I’m reading, it’s not something I look for in a book. If it was really important to a scene to stick, to put that in . . .” she laughs at her own attempt to side-step the double entendre, “if I felt it had to be, I would put it in. But not for this book.”

Well, what about her second novel, just finished?

“No, there’s no gritty sex scene there. There’s mentions of it; it’s real life, there’s sex in there. But there’s nothing about throbbing members or anything like that. It doesn’t go into that kind of detail.”

That’s the downside of being who she is. Having Bertie Ahern as her father, and a Westlife wife as a sister, helped swing the £200,000 publishing deal with HarperCollins, but it also limits what she writes.

“If I really really really wanted to put it (sex) in there, I would, but there would be that extra ‘oh my God, look what the taoiseach’s daughter has done’, and that would be really embarrassing,” she admits.

Certain types of character are not going to appear in Cecelia’s books either. The father figure in PS, I Love You is an anonymous, harmless bloke called Frank, who likes gravy.

“When I wrote it first, it wasn’t for anyone. The only people reading it were my mom and sister, so that was even more of an incentive not to put them in,” she says. “They would have said, ‘What am I doing in your book, take me out’. Then when I found out it was being published, if there were any similarities I would definitely have taken them out.”

There is a personal connection in the novel, though: Westlife. Implausibly, 30-year-old Holly is a fan.