Chris Loveday is 6ft 4in and in his soft brown eyes it is still possible to see a trace of the livewire dad he once was, chasing around with his children, Daniel, now 23, and Holly, 19, on weekends away.

“I remember him teaching them to ride bikes,” says his wife Marilyn. “He worked hard, worked long hours and those weekends were very precious.”

Loveday, a former IBM computer engineer from Northamp-ton, is 55, the age at which he had planned to retire. He and Marilyn were going to take off and see the world. Instead, they are virtual prisoners in their own home.

At 47, Loveday began to develop Alzheimer’s disease. His condition has deteriorated so quickly that he can no longer even hold a cup. Marilyn dare not leave him in case he falls or burns the house down. He is doubly incontinent and needs changing several times a day. At night, sometimes he sleeps, but will just as often be up wandering or banging doors.

“Alzheimer’s is such a cruel disease, cruel for the one who has it and cruel for everyone around them,” says his wife. “This should have been the best time of our lives but instead it is a living nightmare. You live minute by minute. Sometimes Chris can smile and I think: yes, he knows me. But he could turn round the next minute and hit me. The disease makes him aggressive but mostly I get no response at all. He just looks around blankly. It sounds selfish but I’m 54 and I sometimes think: where’s my life?”

There is no effective treatment for someone like Loveday, which is what makes dementia so frightening. He has medication to calm his aggression and sleeping pills to help him try to get some rest. If a drug that could reverse the disease came along, “it would be all I could ever wish for”, Marilyn says. “If I could have even a small part of the old Chris back I would be ecstatic.”

Which is why there was so much excitement last week when Professor Claude Wischik of Aberdeen University announced the results of trials of a drug that appears to slow the progress of early-onset Alzheimer’s by up to 80%. If Loveday had taken the drug in the first months after being diagnosed he, and Marilyn, might have enjoyed another 18 months of relatively normal life.

Rember, the drug that Wischik and his colleagues have developed, is the first to attack directly the “tangles” that occur in the brain cells of those in the early stages of Alzheimer’s. The tangles, made of a protein called tau, strangle and kill cells, first in the memory-critical part of the brain, causing confusion and memory loss, then spreading through the rest of the brain, triggering more general physical decline.

In the first 24 hours after the research results were announced, Wischik received more than 100 e-mails from desperate people living the half-life of the Lovedays all over the world, wanting to join his next trial. One family even offered to move from California.

“It just shows the need to come up with a treatment which is cheap and can be widely used,” Wischik said. “I’m a baby boomer and my age group faces horrendous problems. We’re going to live longer and the risk of dementia rises inexorably with age.”

Of the 10m people over 65 in Britain, a large proportion have Alzheimer’s. The World Health Organisation calculates that by 2050 there will be more than one billion people aged over 65 worldwide.

The government has belatedly cottoned on to the looming cost to the National Health Service and will be launching its National Dementia Strategy later this year. It will aim to increase awareness and improve diagnosis and quality of care, but what boost there will be to research is unclear. According to the Alzheimer’s Society, £13 is spent on Alzheimer’s research per sufferer per year, compared with some £289 per cancer patient. “If we were spending £130 instead of £13 on each patient, we might have had this advance years ago,” said Andrew Ketteringham, its director of external affairs.

Interestingly, the area of research that has produced this new breakthrough was regarded as a backwater in the scientific world. Since Alois Alzheimer, a German neurologist, first described the disease just over 100 years ago, attention has been concentrated on amyloid, a substance that occurs naturally in the brain but overproduces in Alzheimer’s sufferers, creating sticky clusters that turn into plaques which destroy brain cells.

“The little world of Alzheimer’s disease research has been obsessed with the amyloid theory and has been saying for years that tangles – the things Alzheimer discovered – are late stage, you couldn’t access them pharmaceutically, all of which is just false,” Wischik says.

“People would reject our papers. They’d say, ‘Yes, this is all very elegant work but it’s got nothing to do with Alzheimer’s disease, everybody knows that Alzheimer’s disease is caused by amyloid’.”

For the people who have been on the trial the scientific details are irrelevant. What matters is that Rember seems to work. Sandra Sutherland started taking it, as one of Wischik’s 321 “guinea pigs”, almost three years ago, three months after being diagnosed with Alzheimer’s, aged 58.

Sutherland, from Aberdeen, grasped the implications immediately. Her father, William, died of the disease in his seventies, a diminished remote representation of the strong vibrant man she had known. So she knew what Alzheimer’s would bring.

“My father didn’t know people in the end. He didn’t recognise anybody,” she says. “I just automatically thought that would be me, that I would go the same way.”

Following her diagnosis, Sutherland’s mental faculties began to decline, so much so that she stopped driving and left her job in accounting. If she was out she often forgot her address and could not tell a bus driver her destination. She would pick up the telephone and forget whose number she was dialling or begin to write a letter and then lose her train of thought. “I felt scared,” she admits, “and insecure.”

Then her doctor told her about the drug trial and she started taking six capsules of Rember a day. Her husband Ian and their two grown-up sons Gavin and Sean began to notice a difference. She didn’t forget what she was saying mid-sentence as often as she had done, she became an avid gardener and she continues to do a daily crossword. “I slowly got my confidence back,” she says. “I’m not frightened of the future now.”

There are still days when she feels such bone-deep exhaustion that she can only lie in bed and she occasionally lapses: one morning last month, Ian was making breakfast when Sandra walked into the kitchen and began preparing the evening meal. She put a large steak intoa frying pan and cooked it, oblivious to the time of day. “I was making an early start,” she says.

For now she can find some humour in the situation. But she, like the other patients on the trial, knows that Rember only slows and does not halt the effects of Alzheimer’s. Many are worried by the prospect of coming off the drug, but Wischik says that Rember will continue to be supplied on a compassionate basis. However, it will be several years and more trials until it is widely available.

There has been no effective treatment, let alone a cure, for Alzheimer’s so far. Several months ago there was an outcry when the National Institute for Health and Clinical Excellence ruled that Aricept, Exelon and Reminyl should be denied to patients with mild Alzheimer’s. Those who had benefited from the drugs called the decision “criminal and unjust”, but doctors are divided over their efficacy.

A study earlier this year concluded that dementia is now the greatest fear of the over55s. Terry Pratchett, the bestselling author of the Discworld fantasy series, was diagnosed with Alzheimer’s last year, aged 59. He spoke movingly about having a disease that “strips away your living self, bit by bit”.

“I’d like to die like my father did, of cancer, aged 86,” he said. “Before he went to spend his last two weeks in a hospice he was bustling around the house fixing things. He talked to us right up to the last few days, knowing who we were and who he was. Right now, I envy him.”

Additional reporting: Richard Wilson

Times Recommends

• Tree stump 'shows image of Virgin Mary'
• BBC drops Strictly judge for younger model
• Trafalgar Square 'reduced to a spectacle'