'My head was banged against the wall'
It was not until he was about to sit his GCSEs that one of the teachers at his Torquay school suggested that he could be dyslexic.
"I'd always been told I was stupid," the 28-year-old said. "Teachers said I didn't have any academic acumen. Once, in a verbal-reasoning lesson, the teacher repeatedly banged my head against the wall in frustration."
Mr Digby's story is one of several told in Hiding the truth: I can't read, a documentary being screened on BBC 1 on World Book Day, March 2. In it Mr Digby meets other adults who struggled to learn to read including a 60-year-old who has never read a book and a 35-year-old farmer with a reading age of eight.
"We've got to stop hiding in the shadows," he said. "It's nothing to be ashamed of. Einstein and Leonardo da Vinci had literacy problems, and still did well."
Mr Digby saves most of his ire for those who can but don't read. "I present property programmes, and I go into houses and there are always DVDs in children's bedrooms," he said.
"But, time and again, there are no books. They can't all have literacy problems. If you've got the gift of being able to read, and don't use it, that's disgraceful."
Schools are also promoting the importance of reading, as part of the World Book Day celebrations.
At Edgehill college, in Devon, pupils will exchange uniforms and desks for pyjamas and duvets for a day of bedtime stories.
Silverdell bookshop in Kirkham, Lancashire, will serve pupils ice-cream with jelly bookworms and sugary alaphabet letters. William Salisbury, five, who attends St Joseph's Catholic primary, Kirkham, said: "I like to read when I eat ice cream. Ice cream is nice, and books are nice. But I wouldn't want to eat a book."