I am having one of those “Is it just me?” moments. The kind of moment when someone else’s opinion so dramatically contradicts your own that you begin to question everything you thought you knew.

So: is it just me or was Roald Dahl patently quite a screwed-up individual? I ask because the ITV1 documentary The Genius of Dahl, part of the channel’s Perspectives season, appears not to think so.

The programme begins promisingly enough. Presenter David Walliams - himself the author of several children’s books, as he reminds us repeatedly - points out pertinent details from Dahl’s childhood.

There is the fact that the writer’s father and sister died when he was young, that his home life was lawless and that he hated school. And there is the astonishingly scatological letter 13-year-old Roald sent to his mother. Walliams puts down the letter reverently: “This is the birth of a genius.”

This is where it all goes horribly wrong. Dahl’s genius is presented as a full and satisfying explanation for any of the personality quirks - OK, weirdnesses - he demonstrated throughout his life. But this relies entirely on our accepting Dahl’s version of events as the truth.

So Walliams visits Mrs Pratchett’s sweet shop (now the Great Wall Chinese takeaway) in Dahl’s childhood village, Llandaff. Dahl described Mrs Pratchett as “a small, skinny old hag, with goat’s legs and black fingernails”. Walliams then muses that Mrs Pratchett may have inspired some of the writer’s darkest creations. But, equally, the description could be Dahl’s revenge on the woman who was once responsible for his being caned at school. Or, indeed, a reflection of the way young Roald saw and understood the world.

“People were either good or bad. There weren’t many shades of grey with Roald,” muses the curator of the Roald Dahl Museum. The viewer is left to juxtapose these two episodes; the programme does not.

It is not without any insight. Children’s author Michael Rosen suggests that Dahl’s writing comes from his being physically and psychologically abused at school. “If you exaggerate something, you make it safe,” he says.

And Walliams almost gets there, too. Inspecting Dahl’s writing hut, he says: “It’s all very ritualistic. It’s almost like he’s saying, ‘I can’t create the magic unless I have all these things around me.’”

But then, always, he backtracks swiftly. Instead, we are given cod-insight - “I like to think when I’m swimming. But he probably liked to think while he was walking across these fields” - and Joanna Lumley.

All of which leaves me thinking: there is a really interesting programme to be made here, about writing as a means of coping with personal pain. I wish someone had made that programme. But perhaps that is just me.

Perspectives: David Walliams - The Genius of Dahl is available on ITV Player.