It is not long after 10 o'clock in the morning, and Paul is brewing a morning pick-me-up. In the downstairs toilets of a fast-food joint, he is injecting his first heroin fix of the day. Just a few minutes' walk away the Minister for Justice, John O'Donoghue, is announcing a new anticrime measure, a closed-circuit television system for the Grafton Street area.

Neither the addict nor the Minister is aware of the other's presence. "Will I go in and say hello?" Paul asks when he hears.

When he comes back from the toilets the drug is tugging his eyelids down and slowing his voice. He looks like he might fall asleep on the plastic tray in front of him. Then, in minutes, the cloud clears and it is time to go looking for the next deal.

That first tiny white bag of brown powder, about half the size of a fingernail, had been saved from the night before. He will use at least four more before the end of the average day.

Outside, the city has split in two. In one world office workers brace themselves against the wind and rain with umbrellas and briefcases, shoulders hunched and heads down. In the other, Paul and another addict walk with just as much purpose, everything they own in their pockets, scanning every street for a dealer or another junkie who knows who is selling.

Ten minutes walk from Grafton Street is his usual spot for scoring. His estranged girlfriend and two children live in the area. "I hate them living around here," he says.

A well-dressed young man walks out of a shop towards him. "I've nothing at the moment," he tells him, walking past without making eye contact. "We don't stand around any more," Paul says as he watches the dealer walk away. "If you stand around you get nicked."

Two more circuits around the area and nobody is selling. Paul consults a list of numbers. There are more than 30, all of them drug dealers, most of them mobile phone numbers.

At 11.45 he makes a call from a public phone in a grocery store, watched by a wary security guard. Fifteen minutes later a woman, carrying the deal in her mouth, meets him at the arranged spot on a street corner.

The two £10 bags are wrapped together, and as he tears the wrapping open the wind whips one of the tiny scraps of red and white plastic-wrapped heroin out of his hand.

Paul spots the deal and reaches down to cup the leaf where it has landed in the small plot in front of a fashionable Victorian southside red-brick house. Even the most run-down houses on this street sell for £200,000. He plucks the heroin off the shrubbery with one hand and slots it into his mouth with the other. If he is arrested he can swallow the evidence.

It has been just over two hours since his last turn-on, TO they call it. So it's time to cook up again. This time he climbs in behind bushes in St Stephen's Green and puts his syringe behind his right ear. He has filled it with water from a nearby tap.

He has three spoons folded in tissue and wrapped in a spectacles case, a bag of citric acid and a clean "spike" or needle.

He empties every last grain into a small mound in the bowl of a teaspoon. Around it he sprinkles a tiny ring of the white citric acid and then adds enough water to fill the spoon. There is no rushing this. Each movement is carried out with calm deliberation, the spoon balanced on his knee.

As he heats it with a lighter the powder dissolves and starts to bubble. He suctions the liquid into the syringe through a cigarette filter, screws on the needle and squirts a drop of the tea-coloured mixture into the air. "That's what everybody's going mad for," he says. "It's mad, isn't it?"

After 14 years as an addict he has collapsed the veins in his arms, legs and feet. So he turns his back, unbuttons his jeans and injects straight into his groin.

Earlier he had said a garda had told him somebody was selling heroin mixed with rat poison. "He told me to be careful. The problem is the poison looks like gear, smells like gear and cooks like gear."

But there is no safety check on the substance he has just pumped into himself. His only benchmark is whether it is pure enough to keep the withdrawal pains away.

He spits into the syringe to rinse out its bloody residue. "I don't do it for the buzz now. I do it to be normal, so I can walk around, just normal like you are now. Do you need a cup of tea to get you going in the morning? That's a cup of tea to me." He says he just feels warm.

BUT that won't last. The effect of the second fix is less noticeable, and we keep moving. "They call that the drug bus," he says pointing at the 78A serving Inchicore. But things have quietened down in St Michael's Estate, he says, since Garda lookouts have been placed on the roofs. He chooses another bus, heading northside.

"Are ye looking?" the woman asks within minutes of his arrival.

"Two for 25 and four for 50," she says.

He mimics her later, making her sound like a street fruit-seller. He splits the cost of two deals with a teenager eating chips. Nearby, another dealer has arrived and a crowd of teenagers gather.

It is a longer wait for a bus back to the city centre than it was for the dealer. On the journey a young woman gets up to carry a toddler back to her seat. A joint dangles out of her mouth above the child's head, and the smell of the cannabis fills the back of the bus.

Within an hour we are back in another fast-food restaurant for tea and a TO.

"It's a real shooting gallery down there," he says when he comes back. There are four others doing the same, two women and two men.

Back in St Stephen's Green he takes some pride in the fact that the main area the addicts use to shoot up is kept comparatively clean. There are a few swabs, and the discarded plastic wrappings, but no needles. In a tree trunk somebody has left a bottle of water and the base of a soft-drink can that they have used as a makeshift cooking spoon.

Paul says he got his first heroin deal free when he was 13.

"Someone just handed it to me with some foil and said: `Here, try that'."

He has been a dealer himself. He says he travelled to Manchester and Amsterdam to buy small consignments, and employed up to 25 addicts to sell for him. But his own habit took a grip and in the last two years he has become a chronic user.

One day he injected himself 44 times in 24 hours. The following day he just did it four times and he says there was no difference between the two experiences.

Shortly after 4 p.m., less than an hour-and-a-half after the last hit, Paul and his friend go to cook up and inject in a private car-park. This heroin was bought from a passing dealer near the park.

The office workers smoking cigarettes outside their building watch two figures hunched over flickering lighters in the shadows. "There they are," a woman's voice says loudly. The addicts ignore them. Last week the office and restaurant workers called an ambulance for one addict who had overdosed.

It has been an eight-hour day for the addicts, complete with tea-breaks. They will beg or "tap" for a while now to try and make the money for the next fix. His friend has been told he will have to wait until after Christmas to get on a methadone programme.

Paul says his father has warned him that he is living by the gun and he will die by it. It is a brutal and ugly way of life, but there are moments of kindness. A girl in a restaurant gives him an extra doughnut without a word. Shopkeepers give them newspapers, and Paul says he once found a £100 note pushed under his cardboard as he slept. A schoolgirl gave him a fiver this week.

The gardai address him by name and he tips off a new security guard that two "junkie dippers", or pickpockets, have just walked in. That morning a young man in a three-piece suit stepped out of his saloon car beside him.

"Howaya," Paul said.

"Howaya," the young man replied with a friendly smile.

"Freezing, isn't it?"

The two men are about the same age.

"I think I'm fairly intelligent," Paul says over his doughnut. "But society doesn't want me the way I am."