The researchers looked at how many people injected drugs

The researchers found between one in 50 and one in 80 adults aged 15 to 44 in the cities was an injecting drug user.

Writing in the Journal of Epidemiology and Community Health, they say too few clean syringes are available for them.

But the National Drug Treatment Agency said the situation had improved vastly since the period studied.

Hepatitis C fears

Researchers from Imperial College London and John Moores University in Liverpool looked at the proportion of injecting drug misusers in each city and the treatment and assistance which was available in each place.

Drug misusers are receiving treatment more quickly Dr Jenny Bennett, Brighton Drug and Alcohol Action Team,

The team analysed data from 2000 to 2001 from community surveys, specialist drug treatment centres, police data, syringe exchange schemes and admissions for emergency cares.

They found "poor quality" data on the number of people receiving treatment in the three cities, and said the situation required "urgent improvement".

The researchers found that five million syringes are distributed every year in London, 400,000 in Brighton and 560,000 in Liverpool.

This equates to about one syringe being handed out per drug misuser approximately every two days.

But the researchers say most users inject twice a day.

They warn that the shortage of sterile needles increases the risk of disease spread, particularly hepatitis C.

Rates of the disease are higher in the three cities than many other areas in England and Wales.

But the numbers of injecting drug misusers they found there would make the habit as common as diabetes among young adults, and more common than many other chronic diseases, they say.

'Ample opportunity'

The researchers say their findings suggest routine statistics on drug misuse do not accurately reflect the actual prevalence of the problem in the population.

They also estimate that in Brighton around 1% of injecting drug users die from an overdose every year.

Professor Mark Bellis of Liverpool John Moores University, who led the study, told BBC Radio 4's Today programme said there had been improvements in treatment programmes in the last few years.

But he said: "I still think there's a huge population of people left who should be engaged in treatment.

He added: "One of the problems we have is getting to people early on when you can have the most effect."

Writing in the journal, the researchers said: "The government aims to double the number of problem drug users in treatment.

"In the three sites there is ample opportunity for this, given that less than one in four injecting drug users are in receipt of treatment at any one time.

"Unfortunately data on the number in treatment was of poor quality and require a urgent improvement."

They added: "Syringe exchange distribution needs to be expanded, perhaps doubled, to reduce the opportunity for sharing and minimise the risk of viral transmission, especially hepatitis C infection."

Treatment waits cut

Figures from England's National Treatment Agency for Substance Misuse show there has been an increase in the numbers getting into treatment programmes, rising from 100,000 in 1998 to 141,000 in 2002/03.

The government has set a target that 200,000 people should be treated per year by 2008.

The NDTA says average waits for treatment have fallen from an average of nine weeks in 2001 to two in 2004.

Paul Hayes, the agency's chief executive, said: "We are on target to double the number of people in treatment by 2008."

Health workers in Brighton said the figures used in the study did not reflect the current situation in the city.

They said that between October 2003 and June 2004 the number of misusers in treatment rose from 462 to 655.

Dr Jenny Bennett, chair of the drug-related deaths steering group, part of the city's Drug and Alcohol Action Team, said: "It's well known that we have a high number of injecting drug users, but our efforts to tackle this are working."