CLOSE YOUR EYES and try to remember the moment in your life when you were most hungry. You are ravenous. The hunger pains are tearing at your belly like crampons on ice. All you can think about is food — but you don’t have any.

If you can identify with those feelings, then spare a thought for Daniel O’Leary-Williams, because he endures them 24 hours a day, 365 days a year, and he will do for the rest of his life. As the result of a series of medical failings, Daniel suffers from permanent hunger, a craving that can never be sated no matter how much he swallows. If left to his own devices, he would eat himself to death.

Two weeks ago, lawyers for Daniel, a bright and friendly 24-year-old from Bristol, reached a £400,000 settlement with Avon, Gloucestershire and Wiltshire strategic health authority over its alleged failure to diagnose and treat a tumour that grew in his brain for at least seven years during childhood.

Throughout those years, while Daniel was losing his sight, putting on stones in weight and suffering from fits, nausea and crushing headaches, the growth was destroying his pituitary gland and hypothalamus, the part of the brain that controls such basic — but vital — functions as appetite and sleep.

By the time surgeons removed the tumour, the damage to his brain was massive and irreversible. “I remember the first thing I said when I opened my eyes after the operation,” Daniel recalls. “I said: ‘Mum, I’m hungry’. And I’ve been hungry ever since.”

Daniel’s problems began when he was five. His mother, Tracey, 42, remembers being troubled by little things at first.

“He would tell me his head hurt and then there were other odd incidents that made me worried,” she says.

“By the time he was around six, I noticed that he was writing his Ps and Qs, Bs and Ds, and sixes and nines backwards. I told his teacher I was worried that he might be dyslexic, but she said he wasn’t.

“He wasn’t growing as tall as other children and the headaches were getting worse. At night he would hold his head and scream with pain and nausea.”

After she begged a sceptical GP to send her son to a specialist, Daniel was seen by a consultant at Bristol Children’s Hospital, but Tracey has since found out from Daniel’s medical records that the aim of the consultation was to “reassure” her. A second appointment was cancelled and rescheduled by Tracey, while the hospital later claimed that a further two appointments were made for the boy, but Tracey was never notified of them.

Furthermore, as Daniel’s sight began to fail, an optician wrote to his school nurse to say that she had found serious irregularities pointing to something other than bad eyesight — but the nurse either didn’t receive the letter or didn’t act upon it. Whatever happened, Daniel’s condition went untreated for years in spite of numerous pleas for help from Tracey.

Eventually, seven years after the problems began, Daniel — by now massively overweight and sleeping erratically because of the pressure on his pituitary gland and hypothalamus — went temporarily blind.

He was taken to hospital but sent away after having blood tests. Five days later, he collapsed and began fitting; he was finally diagnosed as having secondary hydrocephalus and a cranio-pharyngioma, a type of growth present in between 5 and 13 per cent of children diagnosed with brain tumours. It had been there for so long that much of it had calcified. Today, Daniel is a giant of 25st (159kg) and 6ft 2in (1.88m) with size 14 feet. We meet at the National Centre for Brain Injury Rehabilitation, a part of St Andrew’s Hospital in Northampton. A scar runs across his forehead below a head of thick black hair, a reminder of the six operations he underwent to relieve pressure on the brain and save his life. When we shake hands, I feel as if mine might be crushed.