JK ROWLING has mapped out a series of up to seven crime novels featuring her private investigator Cormoran Strike — in a repeat of the approach she took with her Harry Potter books.

The Cuckoo’s Calling, her first book written under the pen name Robert Galbraith, was published last April and had sold fewer than 1,000 copies before The Sunday Times revealed Rowling to be its author. It has gone on to sell more than 600,000 English language copies in hardback and another 1m in eBook form.

The Silkworm, the second in the series, was written before the first was published and will be released in June. Publishing sources say Rowling has been working on the third since last year.

In The Silkworm, Strike, a