He could be any mother's son. Tucked up in a clean, neatly-made bed at midnight, a Tom Clancy novel for a little escapism, a bright light to read by, a cup of tea and a sandwich for a late supper.

The one thing wrong with this picture is that the bed base is a Dublin city alleyway, where a bitter wind sends stylish, laughing couples scurrying from the nearby nightclub for their cars and the comforts of home.

Peter could be one of them. At 24, he's about the same age. With his big, dark, alert eyes, quiet, straightforward manner and air of ordered cleanliness, he looks like any of them. There's not a whiff of alcohol, or a sign of drugs.

This is no stereotypical, ageing, incoherent wino, his shambolic lifestyle punctuated by a series of bottles in brown paper bags. For the tenth time in a few hours, the self-evidently silly thought intrudes: this looks like no homeless person. But he is.

The sight of young men clutching blankets around themselves in doorways is commonplace. Few people want to get any closer.

During one cold week in December, the Dublin Simon Community went out and counted the numbers sleeping rough in the city. It found 151 - a figure large enough to startle even those charged with their statutory responsibility.

Even more startling was the finding that nearly half were aged under 25, that one in four of these was female and that 10 per cent were 16 or under. Over 100 had been on the streets for more than a year, being raped, stabbed or robbed, getting their teeth kicked in, getting their faces stamped on.

Outside the Screen cinema, for the 10 o'clock Simon soup run on Thursday night, nine or 10 of them drift in like ghosts through a mist. There's delicious home-made chicken soup, freshly-made sandwiches, tea and coffee, chocolate and fruit, handed out with huge respect and good humour by Geraldine and Fiona.

David and Tom are there, two 23-year-olds. Tom wants money for an interview (another newspaper gave him £20, he claims) but David chides him softly: "She's only here because she's trying to help us. . ." Dressed like any ordinary young man, in jeans, anoraks and trainers, David's nervous demeanour and haunted eyes are the only evidence of a life out of kilter.

He speaks affectionately and respectfully about his girlfriend and their three children, all under the age of four. Eighteen months ago, he had a job on the buildings, a council house in the suburbs and a heroin habit. "I was into drugs, I wasn't pushing them," he says, "but I had certain friends coming in. . ." Vigilantes took note and moved them on. His girlfriend and two of the children ended up with her mother; the third child is with his mother.

Robbed at syringe point in a hostel and unable to bring himself to spend a night under his mother's roof, he is on the streets. Delve further into why he feels unable to spend a night with his mother and a classic street-child story emerges: of a childhood of such horror that the only surprise is that anyone could survive it at all, never mind with relative sanity.

He was only six when his mother's boyfriend routinely dragged him out of bed at 4 a.m. to lash him with a belt; he was little older when the mother (herself horribly abused) tried to run away and her boyfriend made her return by hanging David out a high window by his heels.

These are only the incidents he cares to talk about: "Even Tom, who knows nearly everything about me. . . I wouldn't tell him some of the things that man did to me. They go round and round my head, never leave me alone. . ."

David's situation epitomises the dilemma of those who speak for the homeless. To get back into normal life, an address is a prerequisite - to apply for a job, to claim the dole, to rebuild their self-respect. But the problem is rarely that simple. Just scratch the veneer and it's evident that drugs and alcohol and general instability are often the manifestations of problems that go back to babyhood, problems of such deep-seated emotional and physical deprivation that only long-term counselling and support could even begin to sort them out.

David yearns for "an address, a normal job, a normal life". His girlfriend brings the children down to Focus Point for visits every few days and they go for a walk together - "like a normal family" - but only if they agree that he looks "reasonably OK".

He claims to have kicked the heroin problem by going "cold turkey" a year ago, and drinks only when the depression overwhelms him. At the back entrance to the Central Bank in Temple Bar, monument to the Emerald Tiger, the security guard waves away the Simon volunteer's car.

Nearby, a young homeless girl who looks no more than 15 or so is under the thumb of a bullying boyfriend. He takes the fruit and chocolate meant for her for himself, resents the time she spends talking when it could be spent begging, and is urging her to sue another newspaper for "breach of privacy".

Not far away, Patrick, a gentle, angel-faced 20-year-old, sits hunched in a blanket, looking at a third month on the streets, another victim of what he calls "the devil's drug" and a dysfunctional family. He did a butcher's apprenticeship, he says proudly, but had been dabbling in ecstasy and hash before being drawn into heroin: "I really didn't think it would be different. . ."

He "sort of" blames his father for throwing him out: "He was always hitting my ma and when I started hitting him back, he used the drugs as an excuse to get me out. . . Only last week, my ma had a big black eye." He spends up to 20 hours a day "tapping" (begging) and claims to make about £60 - enough to fund the "stuff" he gets in Fatima Mansions. His ex-girlfriend brings their seven-month-old baby down to his mother's house twice a week where they arrange to meet and he gets a chance to clean himself up.

There's still a note of hope in Patrick's voice. "I'd like to get off the streets and have a place of my own. I have confidence in myself. I'm starting back on a course at the clinic at Tuesday. I'm going to make it this time. . ."

Near the Liffey, 24-year-old, flu-stricken Mick is sitting in the chilliest place in the city because he knows the gardai won't move him on from here. The corporation claims he and his girlfriend - and their two children - were evicted from their flat and need not, therefore, be re-housed, but that's not strictly true, he says. He surrendered the keys after vigilantes put a shotgun to his head.

In any event, they both now live on the streets, with one child at his mother's and the other at hers. She has been raped, at home and on the streets, and suffered numerous attacks, but is weaning herself off heroin by buying methadone on the black market. Mick, a qualified chef, buys physeptone in the same way (costing £20 a day) and is trying to get on a maintenance course. The irony, he says, is that he'd have to go back on heroin to get the "dirty urines" needed for acceptance.

Like the others, his childhood story is one of daily murderous beatings by his father - beatings severe enough to cause broken bones and smashed teeth. But only a stone could remain unmoved by Mick's account of how his father finally gave up alcohol, which enabled him to seek out his son a few months ago, and - for the first time in their lives - to hug him and say he loved him.

The gut-wrenching sense of loss for what might have been trembles in the silence as one of Europe's coolest, most affluent cities winds down for the night. Back up near the nightclub, Peter puts down the Tom Clancy novel and sips his tea. Orphaned at 15 by an accident in which not only his parents but several family members lost their lives, he went to live in England with his sister, where he had a job and paid his way. A few months ago, he came back to be close to his young brother and sister, recently taken into care after the death of his grandmother.

His story is a typical one of the streets. Robbed of his money in a hostel shortly after his return, and having witnessed a man in the bed beside him lie on a hidden syringe, he refuses to take refuge in a hostel now.

The British system is more humane, he thinks. There, they set you up for a while, "give you a chance to find your feet". He needs to see his brothers, he says, but it's clear that only in England will he get the chance to pull his life back together.