Jason Roberts says some dealers travel from London to sell heroin
The price of a bag of heroin has halved in Portsmouth over the past year, according to a survey conducted by DrugScope.
And no-one knows the extent of the problems caused by the drug better than Dave.
Heroin destroyed the 44-year-old's life.
He became addicted to the drug during a three-year stint in prison for selling cannabis.
"I hadn't tried it before I was inside - I had always looked down on it - but I tried it. It made time fly by, which was ideal," explains the father-of-two.
"I was a regular user by the time I left prison - it just crept up on me. I wish I never started using it. People warned me, but I wouldn't listen. It's the worst mistake I ever made."
The habit prompted his wife to leave him, causing the disintegration of his family.
After being diagnosed with emphysema as a result of his drug use, Dave now lives alone in a bed-sit and is resigned to his condition slowly killing him.
He is just one of more than 1,000 heroin users who have reportedly been targeted by a new breed of dealer on the streets of Portsmouth selling heroin at massively reduced rates.
Research conducted by DrugScope, an independent body that carries out research into drugs, estimates that the price of 0.3g and 0.4g bags of heroin have fallen from £40 to £20 over the past 12 months.
As a result, users like Dave have found it increasingly difficult to kick their habit, while vulnerable youngsters have fallen foul of the drug.
"We have seen a huge increase in clients over the last 12 months," says Jason Roberts, a project worker at Portsmouth's needle exchange.
"Portsmouth is a lovely city and there is not that much crime, but the drugs problem is massive.
"The police are losing the battle against drugs. They don't have a grip on the situation."
But DC Richard Bateman, a drugs intelligence officer with Portsmouth police, believes the problems have been overstated.
"I have spoken to various sources and it seems the prices remain consistent. The half price business is usually an outside - i.e. London based - dealer selling to attract a customer base," he says.
"Once this customer base has been established the price will return to the normal price. This has been a ongoing trait for a number of years."
And, responding to claims that the police had enjoyed little success in their battle against dealers, he goes on: "We are constantly targeting Class A dealers in the area be it they are local or outsiders.
"Heavy custodial sentences have been handed out."
But Mr Roberts, 35, who has worked in social care for 10 years, is adamant that the problem is spiralling out of control.
The DAIS provides clean needles to prevent the spread of diseases
He points out that the needle exchange, which provides clean needles for around 1,000 people, has seen an increase of 40 users a month seeking help.
Portsmouth DAIS - Drugs Advice, Intervention and Skills - was set up two years ago and is funded by the National Treatment Agency.
The project worker agrees with the police that the huge drop in price has been caused by dealers from outside the city, but he also thinks local dealers play their part.
He also believes drugs are routinely smuggled into the coastal city through ports.
Mr Roberts also noted an increase in the number of users injecting heroin and crack, adding that dealers bolstered their trade by circulating business cards with their nicknames and contact details, as well as waiting outside the city's rehab centres.
Workers at the DAIS have seen a number of injuries in the centre, from abscesses in the wrist and collapsed veins in the neck and forehead, to a man's toe falling off when he took off his sock after complaining of foot pains.
But by far the biggest health problem has been the spread of hepatitis C through the sharing of dirty needles - a problem which can lead to cirrhosis of the liver and liver cancer.
Mr Roberts says the aim of the clinic is to "give people the chance to take the drugs in as safe a way as possible so that if they decided to come clean they would be healthy, as well as preventing the spread of diseases through the use of dirty needles".
According to Paul Slade, 38, who runs the DAIS, Portsmouth's heroin problem has been exacerbated by the lack of post-rehab care opportunities on offer, prompting many to return to old habits.
Addicts undergo a two-week detox programme and, if deemed necessary, they can take part in a four-week residential NHS clinic.
In addition to rehab, Mr Slade believes addicts need help to develop "basic living skills".
"They are used to a chaotic lifestyle. They have never gone home and cooked food, or basic functions like that," he says.
"They need life skills; such as help with money management, hygiene and cleaning their clothes. These are things that most people take for granted."