The level of cocaine use in the UK is as high as in the US, a report by the UN's anti-drug body has said.
Cocaine is used by 2% of people in the UK, the UN anti-drug body says
The International Narcotics Control Board (INCB) report said 2% of Britons used cocaine, and the UK had one of Europe's highest rates of cannabis use.
It also said methamphetamine was emerging as the world's biggest drug problem but use remained low in the UK.
The government said it accepted the findings, while the Tories accused ministers of failing on drugs.
The annual report on global drug use said the UK had one of Europe's highest rates of cannabis use, alongside the Czech Republic, France, Ireland and Switzerland, in 2005.
INCB chief Professor Hamid Ghodse said the government's recent downgrading of cannabis in the UK had been a mistake.
He said the UK had historically had a high level of drug use, but that the downgrading was confusing and sent out the wrong message.
Shadow home secretary David Davis said the UK was the "cannabis capital of Europe" because of government policy failings over the declassification of the drug.
He also told BBC Radio Five Live that the government was failing to tackle the problem of hard drugs, and that users should be given a choice of a long rehabilitation course, or "criminal sanctions".
"Drugs are cheaper on the streets of this country than they have ever been," he said.
Professor Ghodse warned methamphetamine - now one of the most prevalent drugs in the US - posed the biggest threat.
Also know as crystal meth, it is a synthetic stimulant which allows users to stay awake for days.
"It has not yet affected that much of Western European countries and the UK but, as we know, as drug misuse occurs in North America sooner or later it gets here," he said.
"Methamphetamine is today's problem drug. We think that it is extremely worrying.
Amphetamines are synthetic stimulants varying in purity
Methamphetamines are a stronger version, usually powder, crystals or tablets
Effects range from increased confidence to euphoria
Users can party for long periods
Side effects include psychological dependence and psychosis
Depression and lethargy can set in during comedown
"It is one of the drugs which can be very rapidly addictive. And it has lots of complications."
In 2005, British authorities seized more heroin than any other European country, the report also said.
It listed other strategies the UK had undertaken to combat drug use, including improvements to the way people are treated for drug addiction.
A Home Office spokesman said it was pleased to see the report's "many positive references to measures taken under the government's strategy on drugs".
He said record numbers of people entered treatment last year for addiction to class A drugs.
"The British Crime Survey shows that the number of 16-24 year olds that have ever taken class A drugs has fallen by 24% between 1998 and 2003/4, and that the use of class A drugs in the past year has stabilised," he said.
On methamphetamine, he said: "Work is under way to improve monitoring of its prevalence, and to make domestic production of the drug harder, while education about the risks associated with the drug has been reinforced.
"These risks are reflected in a five-year penalty for possession, and 14 years for supply."