Britain is now cocaine capital of Europe

It revealed more than 900,000 Britons buy cocaine, which means the country has overtaken Spain as the biggest user in the continent.

In addition, Britain's 350,000 heroin users are the largest number in any country in Europe.

The annual survey from the UN's Office on Drugs and Crime said that across most of the world drug abuse is holding steady or is in decline because of successful law and order campaigns to prevent their distribution, sale and consumption.

But the falling tide in many countries is leaving Britain exposed as a thriving drugs market where millions remain addicted to or repeat users of illegal substances.

The report found cocaine use had gone up in Britain and added: "In absolute numbers estimates suggest that the UK's cocaine market, some 910,000 people, is even marginally larger than the market in Spain, some 890,000 people."

It added "cocaine is now the second most widely used illegal drug in the UK after cannabis".

But it noted that cannabis use in this country had diminished since the reclassification of the drug - from Class B to less serious Class C - in 2004.

The change made it rare for police to arrest anyone for possessing the drug.

The UN said the fall was "probably because extensive discussion about rescheduling cannabis brought new scientific findings on the potential harm of cannabis into the limelight". "Growing awareness of the dangers of cannabis use among young people went in parallel with declining cannabis use," it added.

The growth in cocaine use came alongside evidence that the drug is now available more cheaply than ever before. Drugscope said after a survey last year that prices have dropped to £44 a gram, nearly a third down on £65 a gram in 2000.

Tory home affairs spokesman David Davis said: "This is yet more evidence that Labour continues to fail on drugs."

But Home Office minister Vernon Coaker claimed success in cutting drug abuse.

He said: "I welcome the report which shows that tough enforcement is having an effect on cutting drug use.

"We have achieved a great deal through our strategy of enforcement, early intervention, education and treatment: in England and Wales drug use has fallen by 16 per cent since 1998 while drug-related crime and the harm caused by illegal drugs have fallen."