One of the most popular creations in fantasy literature, Philip Pullman's world of His Dark Materials, is to return in a new trilogy.

The first volume of a new trilogy, The Book of Dust, is to be published on October 19.

The Book of Dust will be in three parts like His Dark Materials.

The author said the book is about "the struggle between a despotic and totalitarian organisation, which wants to stifle speculation and enquiry, and those who believe thought and speech should be free."

The His Dark Materials trilogy sold more than 17.5m copies in over 40 languages.

The new book is set 10 years before Northern Lights, the first volume of that trilogy, and centres on the character Lyra Belacqua.

The book is set in Oxford and London in the same parallel world as before.

Philip Pullman said: "I know from their letters and tweets that my readers have been waiting patiently (mostly) for The Book of Dust for a long time.

"It gives me great pleasure and some excitement at last to satisfy their curiosity (and mine) about this book.

“The first thing to say is that Lyra is at the centre of the story.

"Events involving her open the first chapter, and will close the last. I’ve always wanted to tell the story of how Lyra came to be living at Jordan College and, in thinking about it, I discovered a long story that began when she was a baby and will end when she’s grown up. This volume and the next will cover two parts of Lyra’s life: starting at the beginning of her story and returning to her 20 years later."

He added: "So, second: is it a prequel? Is it a sequel? It’s neither. In fact, The Book of Dust is… an ‘equel’. It doesn’t stand before or after His Dark Materials, but beside it."

James Daunt, Managing Director of Waterstones, said the news was "exhilarating… for those of all ages.

"Other books, other authors, make claims and bring huge rewards… but it is Philip who cements the sophisticated, unique pleasures of reading."

Francesca Dow, Managing Director of Penguin Random House Children’s, said: “The Book of Dust is a story for our time, with themes that resonate with our world today. It is a story for everybody: a much longed-for treat for established fans of His Dark Materials as they meet Lyra Belacqua again and the chance for new readers to step into the magical world of Philip Pullman for the first time."