He couldn't have been more wrong. When it was first broadcast on Radio 4 in January 1997, the play in which the eponymous protagonist reflects on her impending death prompted a huge response. Pick of the Week had its biggest mailbag and the BBC repeated the show within weeks. It has subsequently been broadcast again. Urban legends abound of lorry drivers so engrossed in the tale they had to pull over to the side of the road, and of a doctor who stopped consultations and simply ushered all his patients into his surgery to listen to the play.
The audio tape, released by the BBC Radio Collection, has sold 30,000 copies and picked up six awards, including the Writers' Guild gong for best original radio play. Now Spoonface Steinberg has transferred to television and is on BBC2 on Tuesday as part of a Children's Health season.
What has precipitated this fever pitch of interest? "It's a taboo to have children talking frankly about death," reckons Hall, who was also responsible for last year's highly successful BBC1 film The Student Prince. "Researching the play, I was looking for first-hand accounts of children dying, and I found it really, really difficult. There wasn't anything similar - perhaps that's why it struck a chord. Also, although it's about difficult subject matter, it's not morbid."
For Simon Curtis, co-producer of Spoonface Steinberg, "the short life of a child is always very emotional, but there is something about her optimism and intelligence and the simplicity of it all that is very affecting. You get caught up in the spell of it. The inner world is so much more affecting than a naturalistic, conventional film about a child in that condition."
It is true that the play's power largely derives from Spoonface's piercing vision, voiced with wonderful clarity by 10-year-old Becky Simpson. When admitted to hospital with suspected cancer, she says: "They were all very nice to me. The doctors held onto my hand and stuff, and they all smiled - which means something's wrong."
Hall explains: "I find it liberating to use the voice of a child, because they can be innocent and naive, and they can ask a lot of questions that adults wouldn't ask, and find a lot of answers that adults wouldn't immediately come across. It gives you a broader palette to write from."
Placing a young child in the central role was motivated by artistic reasons, too. "I wanted to use stream of consciousness," says Hall. "Being inside an autistic child's mind gives you the opportunity deliberately to step away from straightforward realism. You can see ordinary events in an extraordinary way. The autism angle made it different and allowed me to heighten the experience. I didn't want it to be mawkish, but something more wild."
The writing is also illuminated by shafts of black humour. At one point, Spoonface discusses her condition with the cleaner, Mrs Spud: "I said I thought I might have caught it off God. She said, 'God does not have cancer, as far as we know'. I said, 'Maybe he's just not telling anybody'."
Spoonface Steinberg was not conceived by Hall as an issue play. "I wrote it as a spiritual meditation. I thought the cancer and autism were secondary, because it's about a person, as opposed to a person with cancer or autism. It's a character study first and foremost. To me, the disabilities were incidental."
The play nevertheless has immense power to move - don't even think of watching it without a box of Kleenex handy. As she muses on her fate, Spoonface hits upon an explanation which is simple yet profound. "If you were going to die, what was the meaning of all the trees and the bushes and the famines and the wars and disasters, and even the pencils and pens?... If you found the spark, then it would be like electricity and you would glow like a light, and find the spark - that was the meaning."
According to Hall, "It's a pantheistic vision of the world. I found it made sense not only of the big things, but also of the small, quotidian things. A child understands that vision."
As the Book of Common Prayer would have it: "Out of the mouth of very babies and sucklings hast thou ordained strength."
'Spoonface Steinberg' is on Tues at 9.50pm on BBC2