When one of Steve Jones's elderly aunts was forced by disabilty to move into a residential home, she left him a substantial flat and a problem. 'Every surface was piled high with rubbish,' he says. 'It was as if nothing that came into the flat ever left it. You moved from one room to another only through corridors of cardboard boxes.'

There were spent matches, flat batteries, used tea bags, old tin cans, enough bottles of pills to stock a pharmacy, piles of polystyrene trays from supermarket meats, bunches of rusted keys from homes left decades ago, every Christmas and birthday card, copies of the Radio Times going back 17 years, every bill demanded and each receipt for money paid: utilities, public and private, rates, community charge and council tax.

The phenomenon is not new; the psychologist William James described it in 1890. Moving in to clear a 'miser's den' in Boston, public health officials encountered 'bushels of such miscellany as is to be found only at the city dump'. Such hoarding was, James wrote, a perversion of the natural acquisitive instinct found in everyone.

We all collect something or other, and the value of much of what we collect is arbitrary. Why should stamps be more sought-after than bus tickets? But there is a point when the inability to dispose of worthless objects becomes pathological. It is a phenomenon doctors have included in what they term the 'Diogenes syndrome'. Whether the ancient Greek philosopher ever lived in a barrel is immaterial. His disdain for an ordered household is legendary.

Mr Jones's aunt had the collecting mania and he had the difficult task of sifting through the debris of her life. But in other respects he was lucky. She did not have the extreme self-neglect that is the other manifestation of the syndrome. In extreme cases, it can lead to piles of rotting food and even faeces and pools of urine among the assembled junk. That is frequently what leads neighbours or relatives to alert the social and medical services.

Sometimes there is clear mental illness, such as severe depression and dementia, or physical disability. But up to half of all people with Diogenes syndrome appear to be reasonably fit. 'Every psychiatrist has two or three such cases on their books,' says Dr Mike Nowers, consultant in old age psychiatry at the Cosham Hospital, Bristol. 'The question is whether these people too are really ill, or just odd.'

It used to be thought that Diogenes syndrome was a personality problem, that these people were just two standard deviations away from the 'normal' collector, and that they chose to live in conditions most of us would regard as intolerable. But it has recently been suggested that the syndrome may be due to subtle damage to the frontal lobe of the brain, an area responsible for much of our ability to plan and look after ourselves.

This distinction is not merely academic; it has implications for what can legitimately and ethically be done to help. Under the Mental Health Act of 1983, people can be compulsorily removed to hospital if they are suffering from a mental disorder (which is not defined) and if to do so is in the interest of their own health and safety or for the protection of others. If there is no such mental disorder, a place in a hospital or home can be offered under the National Assistance Act, but it cannot be insisted upon.

The difficulty was recently raised in letters to the Bulletin of the Royal College of Psychiatrists. While recognising the severity of the problem, correspondents made clear that they did not wish to act as 'agents of social control' who were responsible for 'pitchforking elderly people into institutional tidiness'. But that situation would change if there was agreed evidence of genuine mental disorder.

Dr Nowers is uncommitted about whether organic brain disease or eccentricity underlies Diogenes syndrome. 'It may seem strange to us to sit in squalor, but if that is what people choose to do. What am I to say about it? On the other hand, if you could establish that there is frontal lobe damage then a person's indifference to their state could be seen as part of the problem, and not a true choice. So there is substance behind the debate. Having said that, if I had pounds 1 for every time the frontal lobe had been blamed for some condition or other, I'd be rich man.'

There is now some prospect that the issue will be sorted out. Dr Michael Philpot, consultant in psychogeriatrics to the Lewisham and Guy's Mental Health NHS Trust, hopes to start a systematic study of the 200 or so cases of Diogenes Syndrome known to his local social service departments. He aims to conduct a full psychiatric interview with as many as he can.

'Hopefully, we will have CT scanning of brain anatomy as part of the study,' he says. 'We may also be able to use other scanning to show how the frontal lobes are functioning, even if there is no sign that brain structure is abnormal.'

Until such research is completed, people with Diogenes syndrome will remain in a diagnostic limbo. Where homes are insanitary, social service 'dirty squads' will continue to clean them, only to find conditions deteriorate once the elderly person is back in residence. Poverty seems not to be a contributory factor. A GP in Southampton reported that pounds 15,000 was found among piles of old newspapers in a house lived in by an old lady who chose to dress in rags. So provision of more financial resources is unlikely to make a difference. Other assistance also has little record of success. Even the most hardened home helps give up in despair.

There is a possibility that the hoarding element could be treated using a new class of antidepressants called serotonin reuptake inhibitors. These drugs (of which Prozac is an example) have recently been licensed for use in people with obsessional problems, and collecting mania arguably falls into this category. But Mr Jones's aunt, for one, is unlikely to agree to the need for such treatment. She argues that she has always been just one step ahead of the recycling movement. The need for her tin cans and newspapers has already been recognised. She confidently expects the time will come for her batteries, polystyrene trays and tea bags.

Mr Jones acknowledges the need for care and sensitivity in sorting through the relics of other people's lives. 'Why didn't I junk the lot? Because among all the detritus were things of sentimental value important to family history. My aunt was a gifted diarist and photographer. Some letters and pictures were certainly worth keeping. The least we can expect of those who follow is that they will consider what we have done and conserve anything that may be of value.'