JK Rowling has spoken about the moment she faced her greatest fear as an unemployed single parent, in a new book about the benefits of failure.

The Harry Potter creator, 49, describes being "as poor as it is possible to be in modern Britain without being homeless" after her marriage fell apart four months after her eldest daughter, Jessica, was born in 1993.

Her experience is laid out in the book Very Good Lives, published next month. 

"I think it fair to say that by any conventional measure, a  mere seven years after my graduation day I had failed on an epic scale," she writes, in a preview extract published by the Independent. 

"An exceptionally short-lived marriage had imploded and I was jobless, a lone parent and as poor as it is possible to be in modern Britain without being homeless.

"The fears that my parents had had for me, and that I had had for myself, had both come to pass, and by every usual standard I was the biggest failure I knew."

The new book is Rowling's first foray into non-fiction and the closest to self-help the author has come in her distinguished writing career.

It draws from a seminal commencement speech she gave at Harvard University in 2008, based around the importance of failure and how we can use imagination to better ourselves (scroll down for the video).

Rowling famously rose from impoverished single mother to world-famous author on the back of her Harry Potter franchise. She now has a net worth of £570 million and book sales of 450 million worldwide. 

But she's at pains to point out that this transition was not the straight-forward fairy tale it's been portrayed as; when she hit "rock bottom", she had no idea what lay ahead.

"I’m not going to stand here and tell you that failure is fun," she writes. "That period of my life is a dark one, and I had no idea that there was going to be what the press has since represented as a kind of fairy-tale resolution.

"I had no idea then how far the tunnel extended, and for a long time any light at the end of it was a hope rather than a reality."

So why does Rowling consider failure important?

"Simply because it is a stripping away of the inessential," she writes. "I stopped pretending to myself that I was anything other than what I was and began directing all my energy into finishing the only work that mattered to me.

"Had I really succeeded at anything else I may never have found the determination to succeed in the one arena where I truly belonged. I was set free because my greatest fear had been realised and I was still alive and I still had a daughter whom I adored. And I had an old typewriter and a big idea.

"And so rock bottom became the solid foundation on which I rebuilt my life."

Rowling, who studied modern languages at Exeter university, now lives with her three children and second husband GP Neil Murray, whom she married in 2001. 

As well as contributing towards university-wide financial aid at Harvard University, sales of Very Good Lives will benefit Lumos, a non-profit international children’s organization founded by Rowling to end the institutionalization of children around the world.

"Lumos is a spell I created in Harry Potter that brings light to a desperately dark and frightening place," the author says. "At Lumos this is just what we do: we reveal the hidden children locked away behind closed doors in institutions and forgotten by the world, so that everyone first of all understands the problem and then works together to fix it."

Watch Rowling deliver her original Harvard speech about the benefits of failure in the video, below. 

Pre-order your copy of the book here.

Photos: Rex Features and ThinkStock