Image copyright Fenris Oswin Image caption JK Rowling wore 'my Robert suit' to discuss her alter-ego Robert Galbraith

JK Rowling's crime novels written under the pseudonym Robert Galbraith will eventually outnumber her Harry Potter books, she has revealed.

The author said her plans as Galbraith were "pretty open ended" and that his books would number more than the seven Harry Potter novels she wrote.

The second novel under Galbraith's name was published in June, and she said she was half-way through writing the third.

She was speaking at a rare public talk at Harrogate's Crime Writing Festival.

I think, in many ways, that the Harry Potter books are whodunnits in disguise JK Rowling

Galbraith's novels follow private detective Cormoran Strike, a former military police investigator in the Special Investigation Branch.

Rowling, who began using the pseudonym for her crime writing career after completing the Harry Potter series, said the third Robert Galbraith novel would centre on returning military personnel.

"The next book is quite different," she said. "You find out quite a bit more about what happens to people after they leave the military."

Image copyright Fenris Oswin Image caption Rowling and Val McDermid appeared in front of fans at Harrogate's Royal Hall

Rowling was interviewed on stage in Harrogate, North Yorkshire, on Friday by fellow crime author Val McDermid.

Asked whether it was true that she would write a total of seven novels under the Galbraith name, Rowling replied: "It's not seven. It's more. It's pretty open ended.

"I really love writing these books, so I don't know that I've got an end point in mind.

"One of the things I absolutely love about this genre is that, unlike Harry, where there was an overarching story, a beginning and an end, you're talking about discrete stories. So while a detective lives, you can keep giving him cases."

She added: "I'm about half-way through the third [novel] and I've just started plotting the fourth."

'Golden age'

Wearing a grey suit and pink tie, which she described as "my Robert suit", Rowling told the audience that she started writing under a pseudonym because "I wanted to prove to myself that I could get a book published on the merits of the book".

The author's true identity was revealed last July, three months after Galbraith's debut novel The Cuckoo's Calling was published. "While it lasted, it was a lot of fun," she said of the pen name.

The follow-up, The Silkworm, was published last month.

Asked why she chose to write crime stories after the Harry Potter series, she replied: "I love crime fiction. I've always loved it. I read a lot of it and I think, in many ways, that the Harry Potter books are whodunnits in disguise.

"I enjoy, I suppose, the 'golden age' book. That's very much what I was trying to do in these books - to take that finite number of suspects, the genuine whodunnit style, but make it very contemporary, bring it up to date, and make sure this is a credible person with a credible back story for nowadays."

Film script

Referring to the "golden age", she said she was a fan of authors Agatha Christie, Dorothy L Sayers, Margery Allingham and Ngaio Marsh, who wrote in the mid-20th Century.

"My very favourite of those four is Allingham, and she's the least known," she said. "The Tiger in the Smoke is a phenomenal novel."

Rowling is also currently working on her first film script, for Harry Potter spin-off Fantastic Beasts and Where to Find Them.

"It's been challenging, it's been fascinating, it has been a lot of fun," she said of script-writing. "But as fun as it's been, my first love is definitely novels."