Afghan opium cultivation has reached a record level, with more than 200,000 hectares planted with the poppy for the first time, the United Nations says.

The UNODC report said the harvest was 36% up on last year, and if fully realised would outstrip global demand.

Most of the rise was in Helmand province, where British troops are preparing to withdraw.

One of the main reasons the UK sent troops to Helmand was to cut opium production.

The head of the UN office for Drugs and Crime (UNODC) in Kabul, Jean-Luc Lemahieu, said that production was likely to rise again next year, amid uncertainty over the withdrawal of most foreign troops and the presidential election.

He said that the illegal economy was taking over in importance from legitimate business, and that prices remained high since there was a ready availability of cash in Afghanistan because of aid.

"As long as we think that we can have short-term, fast solutions for the counter-narcotics, we are continued to be doomed to fail," he added.

Mr Lemahieu said there had been some recent successes, including the arrest of leading figures in the drugs industry, but it could take 10-15 years to deal with Afghanistan's opium crisis, even if policies improved.

'Virus of opium'

The report said the total area planted with poppies rose from 154,000 to 209,000 hectares, while potential production rose by 49% to 5,500 tonnes, more than the current global demand.

Half of the cultivation area is in Helmand province.

Meanwhile two northern provinces which had previously been declared poppy-free - Faryab and Balkh - lost that status.

The report called for an integrated, comprehensive response to the problem.

"If the drug problem is not taken more seriously by aid, development and security actors, the virus of opium will further reduce the resistance of its host, already suffering from dangerously low immune levels due to fragmentation, conflict, patronage, corruption and impunity," it said.

But the report said there were some encouraging signs, with police tripling their effectiveness to capture "well over 10%" of production and a growth in services set up to tackle addiction.

The findings of the latest report reverse a decline in production last year attributed to bad weather and disease.

However, cultivation has been rising yearly since 2010 despite government efforts to eradicate the crop.

More farmers have been trying to grow the poppy as the price of opium has been rising.

Afghanistan produces more than 90% of the world's opium.