Britain is the largest cocaine market in Europe, with more than one million regular users of the Class A drug, according to a UN report.

Five per cent of teenagers aged 15 to 16 claim to have tried the drug, and 3 per cent say that they have tried crack, according to the report from the UN Office on Drugs and Crime. It says that 4 per cent of young people have taken Ecstasy and almost 30 per cent have tried cannabis. It is estimated that there are 860,000 cocaine users in England and Wales, and 140,000 in Northern Ireland and Scotland combined.

The quality of cocaine sold on the streets has declined in recent years because of a police crackdown that has pushed prices up and led dealers to increase the proportion of cutting agent. Some samples seized were found to contain as little as 4 per cent of the drug, with the average being 23 per cent.

The findings follow a warning from the charity DrugScope that young people are increasingly taking cocaine with alcohol because it allows them to drink more and still feel sober. Martin Barnes, chief executive of DrugScope, said that those using cocaine in this way were probably not interested in the purity of the drug. “They may not be quite so bothered about what they are buying,” he said.

The UN report said that dealers were diluting their product with agents such as dental and veterinary anaesthetics. These mimic the effects of cocaine but are much cheaper. It said that the increased dilution of cocaine in Britain suggested the establishment of large international trafficking groups trading in cutting agents, which are usually legal substances. In the past, most of the cutting took place while the drug was being trafficked to Britain.

Cocaine use fell from a peak of 2.6 per cent of the British population aged 16 to 59 in 2006-07 to 2.3 per cent last year. Europe’s second-largest market is Spain, followed by Italy and Germany.

Sandeep Chawla, lead author of the report, said: “If you take year on year, there seems to be a decline in this market, but there is considerable cause for concern as the UK has still, in absolute terms, the largest numbers in Europe.”

The report said that a clear downward trend had emerged in the size of cannabis and amphetamine markets in Britain, once the largest in Europe. Cannabis use in England and Wales fell from 10.9 per cent among the population aged 16 to 59 in 2002-03 to 7.4 per cent in 2007-08.

“The decline among youth started several years before the decline among the general population,” the report said.

Alan Campbell, a Home Office Minister, said that the latest figures were encouraging but the Govenment was not complacent. “We are taking comprehensive action to tackle cocaine use, from increased enforcement to reduce the supply, along with effective treatment, education and early intervention for those most at risk. Evidence suggests our approach is working.”

Chris Grayling, the Shadow Home Secretary, said the study showed that the Government was failing to tackle the problem. “This is a really depressing snapshot of the drug problem in the UK,” he said.

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