The UK is the cocaine capital of Europe, the UN said today.
The United Nations Office on Drugs and Crime said the UK was Europe's largest cocaine market - with more than one million regular users.
But its report revealed the quality of the Class A drug has declined dramatically in recent years.
A crackdown on traffickers has pushed prices up and led to dealers cutting even more.
Some seizures by police revealed substances being passed off as cocaine that were only 5 per cent pure.
The UN found dealers diluting their product with cutting agents such as dental and veterinary anaesthetics that mimic the effects of cocaine but are much cheaper.
The World Drug Report 2009 revealed that cocaine use increased dramatically in the UK from the mid-90s, but remained stable over the last two years.
Data given to the UN by the UK's Serious Organised Crime Agency (Soca) shows wholesale prices have risen to record levels.
The cost of a kilogram of cocaine has increased by 50 per cent from £30,000 to £45,000 since 2007.
There are estimated to be 860,000 cocaine users in England and Wales and around 140,000 in Northern Ireland and Scotland combined.
The report states: "The UK thus continues to be - in absolute numbers - Europe's largest cocaine market, with its second highest cocaine use prevalence rate."
The report revealed a concentration of "problem drug users" in the capital, with around a quarter of all problem users in the UK living in London - a total of 74,000 people.
That means around one person in 100 in the capital has a drug problem.
The report also details the supply routes that bring drugs to the UK.
Cocaine is shipped here via the Caribbean or - increasingly - the west coast of Africa.
Heroin comes from Afghanistan on land routes through the Middle East to Europe before it is re-packaged and smuggled in to Britain.
Martin Barnes chief executive of Drugscope said: "Following a sharp rise in the late 1990s, reported levels of cocaine use have remained relatively stable in the UK.
"However, the cocaine market has developed during this period as prices have continued to fall and the availability of the drug increased - this reflects similar trends across Europe.
"The purity of cocaine has been falling for some time, with dealers increasingly using cutting agents - such as benzocaine and phenacetin - which more closely mimic the physical sensations associated with cocaine, such as numbing of the tongue or mouth.
"By using such chemicals, it is easier to pass off the drug as being much purer than it is."
Shadow home secretary Chris Grayling said the study showed the Government was failing to tackle the drug problem.
He said: "This is a really depressing snapshot of the drugs problem in the UK and underlines just how ineffective the Government's strategy on dealing with the drug problem has been."
Home Office Minister Alan Campbell said: "We are committed to tackling cocaine use and to reduce the harm it causes.
"The latest data from the British Crime Survey is encouraging and suggests that cocaine use amongst adults in the UK is starting to fall after remaining stable for several years.
"We are, however, 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."Reuse content