Your debut thriller, The Girl on the Train, has just beaten a record held by Dan Brown by spending 20 weeks in a row at the top of the bestsellers chart. How do you feel?

It’s great to break a record. It’s also, though, a slightly artificial thing, isn’t it? I’m not even sure when those records began, and from an author’s point of view, that’s not the most important thing.

Having worked as a financial journalist, you borrowed money from your family to support yourself while you wrote the book, which must have given it an extra edge?

Yes. If this didn’t work I was either going to have to go back to being a journalist or come up with something completely new to do. It was the last chance.

The story revolves around what Rachel, whose life has more or less fallen apart, sees from the 8.04 at the start of the day and the 17.56 at the end. We get glimpses of London life, but this is not a city novel, is it?

No, it’s more suburban than metropolitan. It felt right to me that that was where these people would be living at this point in their lives. I don’t think I could have set it in the middle of London in the same way.

How did the book start to form in your imagination?

I’ve done lots of train journeys, and I’ve always thought how interesting it would be if you actually got to witness something. Because you never really do – I’ve never seen anything interesting! You look at these houses, and most of the time you never see people; you see things that maybe bring images to mind – for example, toys in the back garden that have been abandoned – and that starts you thinking about something.

Rachel becomes convinced that something she’s seen holds the key to the disappearance of a woman whose life she’s fantasised about…

My original idea was for somebody to witness an act of violence, but then I moved away from that, I decided I wanted it to be something much more ambiguous.

There’s also a huge amount of confusion because Rachel is an exceptionally heavy drinker – a pretty uncompromising aspect of the book. What sparked that?

I’d been interested in writing about somebody who had memory loss as a result of drink for a long time. I read a book about blackouts and the extraordinary things people do [when they have them]...I know from speaking to people that it is a very strange thing. It fundamentally changes your sense of guilt and responsibility if you cannot remember doing something. Even if people tell you that you did it, if you can’t actually remember you don’t feel as responsible, or in some cases you feel responsible for things that weren’t your fault. I thought it was an interesting thing to play with.

Although this is your first thriller, you wrote several novels that might be called chicklit under the name Amy Silver, including Confessions of a Reluctant Recessionista. Why the switch?

The first Amy Silver book was commissioned, and they were not books that came completely from me. They weren’t necessarily the sort of books I read, and although I enjoyed doing them very much, and they were great training, I never felt completely comfortable in that genre. And as I wrote the books, they got darker and darker, and there was more and more tragedy in them. When the fourth Amy Silver didn’t do very well at all, I decided, well, I’ve either got to make a go of this properly, and do what I really want to do, or give it up and get a new career. It did feel a bit like the last chance to get fiction right.

Who are your favourite crime writers? I know you read a lot of Agatha Christie when you were growing up in Zimbabwe.

More recently, it’s people like Megan Abbott, Tana French, Harriet Lane, SJ Watson – there’s so many. Louise Welsh is fantastic, Cara Hoffmann, an American writer, writes really interesting thrillers. I adore Kate Atkinson, her literary as well as her crime output. When I’m writing, I don’t read much crime at all – you don’t want to get distracted by other people’s plots.

Psychological thrillers, often with a domestic setting, seem to be enormously successful at the moment, with Gone Girl the premier example. Does being part of that feel like you’re being pigeonholed, or are you pleased?

I don’t object to being put into that genre. I’m not sure it’s new. I think what happens is, something like Gone Girl does well, and then it becomes a phenomenon and everybody notices it. But crime books in domestic settings have been written for a long time. And it’s these kinds of psychological thrillers that interest me more. If you ever face violence, an awful lot of it is in the home. Those are the concerns that perhaps women face more; if we’re going to be victims of violence, it’s usually in a domestic setting, so those are things we think about a bit more. I’m interested not so much in crime or the act of violence itself but in the psychology of violence, and how we get there.

Now you’re hard at work on your second thriller, which is about two sisters. Is the follow-up daunting?

There is more pressure. When I wrote The Girl on the Train, nobody knew who I was, and that’s quite a comfortable position to be writing in. The new book will have a very different feel in some ways, and similar in others. I’d like to carry over some of that air of paranoia but it’s got a much larger cast of characters, and will be a less claustrophobic book, I think.

Meanwhile, The Girl on the Train looks set to be made into a film.

Yes, DreamWorks has the rights. The director is Tate Taylor, who directed The Help, and they are in talks – I think is the official line – with Emily Blunt, to play Rachel. I’d be very happy with that. I think she’s a wonderful actress. But I’m not writing it, and I haven’t seen the script.

Did you want to be more involved?

No, not really. I’ve not done it before, and I don’t know anything about writing for film. I know some people are very good at adapting their work but I think it would be an extremely risky thing to do for me – and in any case I want to get on with writing another novel!

The Girl on the Train is published by Doubleday. To order it for £10.39 click here