Roald Dahl was born in Cardiff of Norwegian parents. He lived there until he was seven, when a headmasterly beating at the Llandaff Cathedral School persuaded his widowed mother to send him to an English boarding school. “English schools are the best in the world”, Dahl recalls his father saying. “Better by far than the Norwegian ones. Better even than the Welsh ones. ” The family left Wales when Dahl was 13.

When it comes to Welshness, we’re not exactly talking Dylan Thomas here. However Dahl’s pre-teens are reason enough for Cardiff Marketing Ltd to lay claim to him as one of Cardiff’s own and it is promoting a six-week series of “Roald Dahl celebration events” running to October 7.

It would all be more dollops of heritage kitsch had Cardiff Marketing not attracted top Dahl-industry figures. My nine and 11-year-old daughters enjoyed an exhibition of original Quentin Blake illustrations; next Sunday we might make it to Prunella Scales and Timothy West doing a live version of their classic recording of Revolting Rhymes (These two events demonstrate that artistic genius such as Dahl’s often stimulates the best from other artists).

We did watch the Sherman Theatre’s new adaptation of Dahl’s autobiography, Boy. “Ex-cell-ent,” said Dora. “Exactly to my memory,” said Kate and there’s no higher praise for a script by Mike Kenny which remained faithful to a subtle text where the 67-year-old Dahl often reminds readers that his memory was flawed. Libel actions have been threatened over the provenance of particular thrashings in Boy.

Yet no jury could doubt the regular occurrence of brutal events which the book, and now play, unfurl as “some awful pantomime”. The mythic, emotional truths are there and it is those that stick in the memory. Kenny hasn’t expunged Dahl’s indifference to his Welsh heritage nor has he done any more than the original text to underline the writer’s debt to Celtic fantasy and story telling. It’s there in the figure of Thwaites, a boy who tells a long tale of how liquorice is manufactured from mashed rats. Where Dahl had a Welsh gift for anecdote, he had a heaven sent gift for seeing the world through a child’s eye. It is the world most of us forget, one where grown ups appear as dangerous giants. Good adults, like Miss Honey in Matilda, and in The BFG, are childlike in their openness but the rest of us . . . especially parents, teachers, doctors and other experts . . . are disgusting and untrustworthy.

Varieties of sadism toward children change with fashion, and thrashing, I would suggest, has been replaced by an oppressive concern with educational achievement. What is undeniably constant is that children are smaller and weaker than adults and Dahl imagines worlds where children have power. The mental atmosphere he evokes, the isolation, fear, hilarity and anarchy, are what makes his books more than period pieces. Dahl attacks schools with a ferocity that hasn’t been approached since Dickens, and does it with such a light touch that people don’t know they’re being mauled. How else could such subversive books be required reading in schools the world over?

Those who try appropriating as powerful a writer as Dahl run risks. Take the Llandaff Cathedral School. It doesn’t actually advertise that Dahl was an old boy but clearly hopes to exploit an association by leaving copies of its brochure in the Sherman foyer. It pictures dinky uniforms which are similar, if not identical, to those we saw on stage. Dahl mocked school uniforms and would have appreciated that the clothes in the play were part of what children in the audience were laughing at. That’s what happens when literature is used as a heritage sales tool; it’s liable to turn round and deliver a kick in the shins.

Boy is at the Sherman Theatre Cardiff until September 30 then tours until early November. For more details on this and other Dahl events, contact Cardiff Marketing on 01222 667773.