You can’t move for stories on the Isles of Scilly, and on Bryher in particular. The children catching the ferry to the primary school on Tresco all look as if they ought to star in a salty adventure yarn laced with local history and ancient legend. Thanks to Michael Morpurgo (almost a local author), some of them have.

Helen Pearce, who played Gracie in the TV feature film of Why the Whales Came (“The film company scoured the country for the right girl,” says Morpurgo, “and when they came looking for extras she was here under their noses, living in the house nearest to the beach where they were filming”) is now grown up, married and living in Australia; Charlie Bennett, who could easily be Laura in The Wreck of the Zanzibar (it’s dedicated to her family), is at secondary school on St Mary’s. Like most of the over-11s on the islands, she is a weekly boarder, but she’s coming home midweek for the launch of The Sleeping Sword, the latest Morpurgo novel. This one is dedicated simply “To the people of Bryher, for all the warmth and kindness over the years”.

Charlie is often the first reader of Morpurgo’s typescripts; “I pick up the pages as Mum’s finished typing them”. Morpurgo lives in north Devon but sends all his manuscripts (written in pencil on exercise books, propped up on cushions on his bed) to Marion Bennett for typing. He has spent 20 summers on Bryher with his wife Clare, is having a second boat built there to accommodate his growing grandchildren, and rarely goes home without an idea for a book.“I spend a lot of time here, not so much writing as dreaming - it’s a wonderful place to dream and an extraordinary resource of stories.

“I can’t do what Philip Pullman does and create whole worlds - my worlds have to be connected to the material I’m offered, then I play around with it.”

Three years ago, he picked up a cracking tale: Paul Jenkins of Hillside Farm on Bryher (“He grows the sweetest tomatoes in the entire world,” says the jacket of The Sleeping Sword) had found an ancient sword and mirror in a kist (burial chamber) beneath a field in spring 1999. With King Arthur’s burial place on the Eastern Isles less than an hour away by boat, Morpurgo reasoned, it had to be Excalibur.

The find has caused great excitement among archaeologists: this is the first Iron Age sword found west of the Tamar, and the first discovery in north-west Europe of a sword and a mirror in the same grave. The bad news is that it’s been dated at 1BC and is no more likely to have been pulled from the stone by Arthur than the mirror (the earliest decorated bronze British mirror) is likely to have come from Guinevere’s boudoir. But Morpurgo is not one to throw away a good story. “Artistic licence,” he calls it.

The Sleeping Sword is a Russian-doll tale with stories stacked inside stories. Excalibur is unearthed by Bun Bendle, a Bryher schoolboy who has been blinded and lost his memory in an accident. In a dream in which his sight returns, Bun and his friend Anna are led by six black-clad queens to the Eastern Isles to return the sword to Arthur.

The islanders haven’t yet spotted a likely source for Bun, but you can see the quay from which he caught the ferry to school and where he took a dive and hit his head on a rock, and the cliffs at Hell Bay where he is overcome by despair.

Morpurgo hints that Bun’s obsession with Arthur dates from a previous meeting; that Bun is the unnamed boy in his first Arthur book, Arthur High King of Britain who is saved by the king when he gets lost in the fog on the Gunilly Sand Bar (“You know how dangerous that is, don’t you?” the writer tells the assembled 28 pupils of Tresco junior and infants’ school on the day of the launch of The Sleeping Sword).

The boy’s story frames what has become a classic account of Arthur’s life and heroic deeds. Arthur High King of Britain, which Bun listens to on audio tape, was published in 1994; thanks to more artistic licence, Bun is still 10 years old in the new book, and as courageous and resilient as ever. In a tribute to artist Michael Foreman’s long partnership with Morpurgo (“We’re practically married; he knows what I’m thinking before I’ve thought it”), Bun is also a Chelsea fan. Foreman has illustrated both Morpurgo’s Arthur books, among many others: “It was his idea to do Arthur High King of Britain; it was something he had always wanted to work on.”

The writer’s bond with the Scillies is entwined with his own lifelong fascination with Arthur.“I didn’t like him much when I was young, though. The books about Arthur that were produced for young people in those days used him in a Victorian way to tell you how to behave and never dealt with what is at the heart of the story: that he sleeps with his half-sister, and that’s what corrupts the family and the kingdom. It’s a harsh, harsh story, full of temptation and ambition and the human condition.”

Bun’s story is harsh, too: his anger, frustration and misery at his sudden blindness leads him to contemplate suicide.“I watched my stepfather go blind,” says Morpurgo,“and saw how he dealt with greeting people he couldn’t see and finding his food on the table, how hard it was.”

An intriguing twist in the story points towards Bun’s recovery, but he has already begun to rebuild his life.

Bryher yields funny tales too, including what Morpurgo anticipates will be “a short story to die for”. How did a 2,003-year-old sword that might once have belonged to a female warrior (the grave yielded only one body for the mirror and the sword) end up hidden in a community centre piano at a book launch party, to be retrieved by a panic-stricken archaeologist at 4am? If anyone on Bryher knows the full story, they aren’t saying yet - but Michael Morpurgo will be back this summer with his exercise book, and he’ll find out.

‘The Sleeping Sword’ by Michael Morpurgo is published by Egmont pound;9.99