Sections of British cities are becoming no-go areas where drugs gangs are effectively in control, a United Nations drugs chief has revealed.
Professor Hamid Ghodse, president of the UN's International Narcotics Control Board (INCB), said there was "a vicious cycle of social exclusion and drugs problems and fractured communities" in cities such as Birmingham, Liverpool and Manchester.
The development of "no-go areas" was being fuelled by threats such as social inequality, migration and celebrities normalising drug abuse, he warned. Helping marginalised communities with drugs problems "must be a priority", he said.
"We are looking at social cohesion, the social disintegration and illegal drugs. In many societies around the world, whether developed or developing, there are communities within the societies which develop which become no-go areas. Drug traffickers, organised crime, drug users, they take over. They will get the sort of governance of those areas."
Prof Ghodse called for such communities to be offered drug abuse prevention programmes, treatment and rehabilitation services, and the same levels of educational, employment and recreational opportunities as in the wider society.
He said: "It is crucial that the needs of communities experiencing social disintegration are urgently tackled before the tipping point is reached, beyond which effective action becomes impossible. The consequences of failure are too high for society and should be avoided at all cost."
The INCB's annual report for 2011 found persistent social inequality, migration, emerging cultures of excess and a shift in traditional values were some of the key threats to social cohesion.
Celebrities' use of illicit drugs may also "contribute to a growing normalisation of certain forms of drug misuse within the wider society and in turn can lead to the undermining of social cohesion". But the INCB warned none of the factors "should be seen as leading individuals inevitably into a lifestyle of drug abuse and criminality".
"Whatever the social processes and social pressures at hand, human beings still have the capacity to exercise some element of choice in what they do and what they refrain from doing," it said.
A Home Office spokesman said: "The Ending Gang and Youth Violence report published by the Government in 2011 sets out a comprehensive strategy for supporting local areas to reduce the effects of gang violence. We want to stop young people from joining gangs in the first place through intervention and support to children and families at risk of gang violence."