Author JK Rowling has revealed she spent a week practicing the fake signature of her pseudonym, Robert Galbraith – the name she used for her new detective novel.

The Harry Potter creator signed a few copies of the book under her pen name, after working on the fake autograph.

‘While we can’t verify whether any particular book currently on eBay etc is genuine, any future books I sign in this way will be authenticated,’ she admitted.

‘My Robert Galbraith signature is distinctive and consistent; I spent a whole weekend practicing it to make sure,’ she said.

Miss Rowling also revealed had offers from two TV firms to bring the crime novel to the screen even before she was ‘outed’.

She was exposed last week after publishing a detective tale, The Cuckoo’s Calling, under the name of Robert Galbraith earlier this year.

She has denied claims it was a publicity stunt and said her unmasking left her angered, particularly when it emerged that her cover was blown by a senior figure at a legal firm which has represented her in the past.

Rowling has now pointed out the book was already gathering interest for adaptations and had sold a respectable number of copies. But she said it was becoming ‘increasingly complicated’ to keep the charade going.

She said: ‘At the point I was ‘outed’, Robert had sold 8,500 English language copies across all formats (hardback, eBook, library and audiobook) and received two offers from television production companies.

‘Yet Robert’s success during his first three months as a published writer (discounting sales made after I was found out) actually compares favourably with JK Rowling’s success over the equivalent period of her career.’

Hit: Since the revelation, sales of the book have soared and the printers of the book, Clays, have had to start reprinting the book in large numbers

Writing on a website set up for Galbraith, she said: ‘If anyone had seen the labyrinthine plans I laid to conceal my identity (or indeed my expression when I realised that the game was up), they would realise how little I wanted to be discovered.

‘I hoped to keep the secret as long as possible. I’m grateful for all the feedback from publishers and readers, and for some great reviews.

‘Being Robert Galbraith has been all about the work, which is my favourite part of being a writer.

Rowling, who found fame with the Harry Potter novels, said she had found the experience of writing as Galbraith ‘liberating’

‘This was not a leak or marketing ploy by me, my publisher or agent, both of whom have been completely supportive of my desire to fly under the radar.

‘If sales were what mattered to me most, I would have written under my own name from the start, and with the greatest fanfare.’

Legal firm Russells offered an unreserved apology to the author last week after it found that one of its partners had been the source of the leak after he told his wife’s best friend in ‘confidence’ about Galbraith’s true identity.

Rowling’s first non-Harry Potter book was ‘The Casual Vacancy’