'My grandad had the best ghost stories and all of them were true'

Having carved a niche for myself raising the spirits of long-dead showbiz luminaries ­ Kenneth Williams, Frankie Howerd and the cast of Dad's Army among others ­ I have decided for my fifth solo show to summon up ghosts of a different kind. Non-celebrity spooks, you might say. In my research, I have immersed myself in volumes of classic tales and watched countless hours of video and I can tell you now that the scariest ghost story ever filmed is The Innocents (1962), a faithful version of Henry James's creepy novella The Turn of the Screw. There's a scene where Deborah Kerr shields her eyes against the sun and sees standing among the bulrushes on the other side of the wide, still lake the figure of a woman she knows to be dead. The woman simply stands there, staring across at her, dressed in black, with sunlight glinting off her lank hair. Why is the moment is so horribly chilling? It could be because Miss Kerr had the most expressive eyes in the movies. You see her pupils scanning the distance, then stop to focus on the alien figure in a moment of blank incomprehension; then almost imperceptibly her eyes widen in astonishment and alarm. All this is achieved in perhaps seven seconds of screen time but you are taken into the mind of a woman whom you already know to be at least eccentric, possibly mad. Here lies the secret of the story's power: it is all completely believable. The ghosts may be real or they may be figments of her deranged imagination but it does not matter. In Deborah Kerr's eyes they are there and that is enough.

The secret of any good ghost story is believability. Wild fantasy will not do the trick. Anyone who tells you about the emanation (or UFO for that matter) that appeared to their uncle's neighbour while he was mowing the lawn must preface the tale with the words: "And he was the most rational, level-headed person you could ever wish to meet." If he were anything else the story would not be worth telling.

Now my grandad, Arthur C Hodgson, had the best ghost stories ever and all of them were true. He was a pillar of his community, I might add, his feet firmly planted on the ground. (Like all pillars of communities he had another side: after he died, his second wife discovered a standing order from his account to a woman in the Black Country, the same woman whose name had been cursed by my granny late one night in 1948 as she sent a plate of coagulated hotpot whistling past his ear.) Naturally I believed him when he told me that he sometimes felt my great-grandfather's hand on his shoulder, comforting him in times of stress. I believed him when he told me he had a painting with a ghost in it: if you looked at it with half-closed eyes you could just about make out, standing to the right of the two ladies chatting outside the cottage, a figure in a long dress and a purple shawl.

There was a ghost who caused an otherwise inexplicable scent of lavender that sometimes wafted through his box room. And one night he had been driving from Dudley ­ where he was headmaster of the Wren's Nest School ­ to the Lake District in his old Austin A40 when a hideous wild-eyed crone had leapt from the shadows and run in front of his car waving her arms, causing him to swerve violently and screech to a halt. He got out and searched the road but there was no sign of her. Shaken, he continued with his journey. But hours later, just outside Keswick ... the same thing happened again! The SAME hideous, wild-eyed crone appeared in his headlights. And of course, when he got out and looked there was nothing to be seen.

Once he told me that he had a friend who had found a whistle with the words "who is this who is coming?" inscribed on the side in Latin, and that when the friend had blown the whistle he had been visited by a ghastly apparition made of sheets which pursued him down a shingle beach and attacked him in his hotel room.

Years later, I discovered that the story "Oh, Whistle and I'll Come For (To) You, My Lad" was written by the Victorian master of ghost fiction M R James, almost all of whose stories are about level-headed academics getting a spooky fright. The truth is that, though he may have been a respected figure of authority to generations of Dudley schoolchildren, Grandad seldom let veracity get in the way of a good yarn.

Twenty-five years after his death my Grandad still visits me in my dreams, looking much as he did the last time I saw him: tired and pale, but doing his best. I had taken the afternoon off from school, feigning a migraine in order to escape the hated A-level European history lesson. He arrived at our front door unannounced, having driven down to Birmingham from his home in Cumbria, with his wife. He swore blind that he had called to let us know they were coming. But he hadn't. Only a week before he had sent my brother and sister a pair of china piggybanks. They arrived in smithereens loosely wrapped in sheets of floral paper. So unlike him, always a meticulous wrapper of packages; clearly there was something wrong. He spent much of his visit coughing in the bathroom. And yet ­ how guilty I feel about it to this day ­ I can still hear him saying during our last face-to-face conversation: "Oh, I'm all right. But what I want to know is, how are you?" He was terribly concerned about my migraine and all too easily I maintained the lie.

I have found out some things I didn't know about him in the course of my research for this show: that he had a dread of lung cancer. That when he was finally diagnosed with an inoperable tumour he went into complete denial about it, assuring his wife that it was just an abscess and that he would be right as rain in a few weeks.

And one last ghost story that he could not bring himself to tell me: not long before the fatal diagnosis they had gone shopping. She had popped into the supermarket and he had waited outside. She re-emerged to find him trembling and white with terror. It seems a hideous, wild-eyed crone had come up to him and muttered some words that struck the fear of God into his heart: "You haven't got long to live." And then she disappeared. And that's a true story.

'David Benson's Haunted Stage': Assembly Rooms (0131 226 2428), Fri to 30 Aug. Contact David on david@thinknoevil.com