“My partner Marie got up at 4am to go to work, so I’d write between 6.15 and 7.30 every morning before going to teach. Carolyn Whittaker, who was the only agent I approached who didn’t turn me down, and she never earned a penny from me for ten years while I was trying to write for adults. So, like Tom, I had a long apprenticeship,” says Delaney, wryly.

Tom, the narrator of The Spook’s Apprentice, is no eager wand-waver but a surly young farmer’s son too many. “I married your dad because he was a seventh son. And I bore him six sons so that I could have you,” his Mam tells him sternly. The Spook is a grim old man armed with salt, a silver chain and a staff, called upon to protect communities plagued by poltergeists, ghosts and above all witches. He needs to train up his replacement to (naturally) save the world. Tom experiences blood-curdling adventures, aided by Alice, a fierce young witch whom the Spook warns him against (“never trust girls in pointy shoes”) but with whom he gradually falls in love.  

Delaney, the son of a labourer, was born into a family of four boys, all of whom shared the same nightmare of an evil creature attempting to carry them off into the coal hole of their two-up, two-down terraced house. Convinced that they would die if it succeeded, the brothers had a pact to wake each other up when one of them dreamt of this. Delaney’s own appetite for reading fantasy was fed by the public library at Preston, but he served as a reluctant apprentice to an engineer for five years before taking three A-levels at night-school and going to Lancaster University to read English. A teacher for 29 years, he eventually became Head of Film and Media Studies at Blackpool Sixth Form College – specialising in vampire flicks.

A lively, grey-bearded man of 62, he began The Spook’s Apprentice as a tale about a con-man who removed boggarts for money, but it changed. Now the world he describes in clear, vivid prose seems to flow unstoppably from his pen. (His wife Marie, with whom he has three children and seven grandchildren, types the books out from longhand.) Every Christmas since 2004 he has delivered a new Spooks book, which then goes through seven or eight drafts with his editor, Charlie Sheppard.  Like JK Rowling, Eoin Colfer and Philip Pullman, Delaney blends folklore with myth, though as he points out indignantly, “my boggarts are the real thing, being basically poltergeists described in Lancastrian histories.”

He uses details from the famous 17th century Pendle witch-trials - but the bleak moor nearby, with its sinister row of human-shaped hollows carved in stone, is equally inspirational. The Spook’s garden (where witches are buried alive in iron chains, waiting for just one drop of human blood to revive their powers) and his even creepier cellars, are in the great, dun-coloured mountains through which the Spook and Tom must tramp, or run for their lives, pursued by horror.

“I think the appeal of the books is that it’s a universal story, and everyone thinks it’s set in their own landscape. I never call it Lancashire, just the County, though it uses many of the old names for real places,” he says. Success has meant that the Delaneys can move out of their present home to Chipenden, the location of one of the Spook’s homes – which, he assures me, is now “a lovely place for those in search of peace and quiet.”

Tom’s beloved Mam is, of course, based on his own mother who died just before the first book was published. Tragedy and moral choice are part of the series’s richness. Alice is a witch, but, as Tom realises, “neither wholly good nor wholly bad.” The misogynistic Spook turns out to be in love with a lamia witch himself (the sort Keats described), and Tom’s own Mam, brought back from Greece, where she was found chained to a rock, has a dark past as well as three mysterious boxes to be opened in direst need. In Spook’s Battle we discover what is in them at last. Delaney himself didn’t know their contents, but the answer is both satisfying, and deliciously scary.

Like all the best children’s literature, the novels are about children discovering the secrets, responsibilities and spiritual mysteries of adults. It’s no surprise to learn that Delaney was educated by Jesuit priests, though he lost his faith when he fell in love with a Protestant.

The fifth book is already completed, out of a scheduled six, but happily there will probably be at least another three to come. Whether or not its author becomes as rich as Rowling, this compelling new series deserves a place on every confident child’s shelf.

The Spook’s Battle by Joseph Delaney is published by Bodley Head this week.