Yet despite these results, the government's new White Paper on drugs policy contains no firm pledge of fresh cash for treatment beyond promising that the £5 million in assets seized each year from drug traffickers will be used to tackle the drugs problem.

There are thought to be more than 100,000 "problem" drug users in Britain. Each one spends around 200 per week on drugs, largely financed by petty crime. A team at the Maudsley Hospital in south London, led by Michael Gossop, identified 1075 such people.

Most were heroin addicts, although many also had problems with other drugs and alcohol. Their treatment mainly involved substituting prescribed methadone for illegal heroin, or residential programmes encouraging total abstinence.

A year after the start of treatment, Gossop's team interviewed 769 of the addicts. On average, their use of street heroin had plummeted. Nearly 70 per cent of those on residential programmes had been taking the drug once a week or more. After a year, this had dropped to 40 per cent. For those on methadone programmes, the number using heroin weekly fell from almost 90 per cent to less than 60 per cent.

The rate of burglaries and other thefts committed by the patients fell by almost half. This is similar to results from US studies ( "Methadone: crime cure or therapy?", New Scientist, 1 October 1994, p 36). But it wasn't a foregone conclusion, says Gossop: "There really are big differences between the drug users and the treatment services."

The White Paper stresses the value of treatment. But groups working with addicts say more money is needed. "The drugs strategy, while good in intent, needs backing with a cast-iron guarantee that the extra resources will be there," says Roger Howard, who heads the Standing Conference on Drug Abuse.