"I love writing these books. One of the things I love about this genre is that - unlike Harry [the Harry Potter series] where there is an overarching story, here you are talking about discrete stories. So as long as your detective lives you can give him cases."

The third novel, which she is a third of the way through, will be "quite different" - "You find out quite a bit more about what happens to people after they leave the military," she said, adding that she had had "a lot of information" on the subject from people who prefer to remain anonymous.

Meanwhile she "loved" the character of Robin, she revealed. "I think Robin is the most entirely loveable character I've ever written. A good person but likeable - a smart woman, a kind and loyal person."

The author said it was a "no brainer" for her to write crime novels, describing the Harry Potter novels as "six whodunits and one whydunit" - and admitting her "dirty secret" - that she never reads fantasy.

On the subject of why she had chosen a pseudonymn and first published The Cuckoo's Calling with no clue as to her true identity, Rowling said: "I wanted to prove to myself I could get a book published on the merits of the book. A friend said, 'Why do you need that validation?' You probably have to be a writer to understand it... I wanted something that was just for me. While it lasted it was a lot of fun." She revealed that she was "jumping up and squeaking for joy" when McDermid's very favourable review of the book was published, and that she even wrote a thank-you letter to McDermid in the person of Robert Galbraith.