The UK had the largest rate of heroin seizures and the third highest number of heroin addicts in Europe in 2004, the UN has warned.
Afghanistan supplies around 90% of Europe's heroin
It said increased production in Afghanistan, where most of the UK's supply came from, had not helped.
UN drugs watchdog the International Narcotics Control Board found the UK had Europe's highest amphetamine usage and the third highest for ecstasy.
Cocaine abuse in the UK had also risen despite stabilising in Europe, it said.
The rate of ecstasy use was higher only in the Irish Republic and the Czech Republic.
In the INCB's annual report, president Professor Hamid Ghodse repeated concerns expressed in last year's report that the British government's reclassification of cannabis from Class B to Class C could send the wrong message to some users.
But the reclassification did not break international drug treaties, he said.
Professor Ghodse warned that Afghanistan was in danger of becoming a "narcotic state" after producing its largest annual crop of heroin - 4,200 tons - since the overthrow of Taleban rule.
He will call for international help for Afghanistan's drugs problem at a press conference in London on Wednesday.
"The board is asking the international community to help Afghanistan in this - it can't happen in isolation," he will say.
"The Afghanistan government needs to do something very serious, very quickly."
The INCB warned the expansion of the EU could weaken border controls and hinder efforts to reduce drug trafficking.
Europe's drug use
Most Ecstasy abuse
Most amphetamine abuse
Source: International Narcotics Control Board
Some 90% of the heroin consumed in Britain and Europe comes from Afghanistan's poppy fields.
Since allied forces ousted extremist Taleban rulers in December 2001, opium production has increased 20-fold.
Tackling the drugs trade is a key element of UK policy in Afghanistan.
Training an elite police unit to go after heroin labs and traffickers has been one course of action.
However, drug education charity DrugScope said it was "too early to say" whether increased opium production in Afghanistan was "fuelling any growth in figures in the UK".
Petra Maxwell, from the charity, told the BBC it took around 12 to 18 months for opium harvested in that country to materialise as heroin on the streets of Europe.
She they are "still waiting to see" what its effects in the UK would be.
She added that heroin use and other drug use in the UK has stabilised.
"What we are looking at is not necessarily a problem that is getting worse very quickly, it has stabilised to a large extent," she said.
Ms Maxwell said recent crime figures had also shown a 20% fall in ecstasy use.
She said the UK's drug problem had to be dealt with not only by cutting supply from countries such as Columbia and Afghanistan, but also by cutting demand.
"We also have to work hard at reducing the demand in the UK, because when there's no demand for a product, there's no money to be made."
Foreign Secretary Jack Straw announced last month that the government would double its aid to Afghanistan for fighting the country's drugs trade.
He said Britain would give around £52m to counter narcotics programmes in the country over the next financial year.
Half of the money will be devoted to schemes to provide opium poppy farmers with alternative sources of income.
Mr Straw made the commitment after talks with the Afghan president Hamid Karzai in Kabul.