'Club drugs' in vast quantities – and even heroin and cocaine – are being delivered by post

Britain has become an international hub for websites selling legal highs with postal workers operating as unwitting "drug mules", according to a report into the burgeoning trade.

The report, which describes the UK as the "addicted man of Europe", says that "club drugs", such as salvia and green rolex, are being bought online in vast quantities and delivered throughout the UK by mainstream postal services.

One in 12 young people have tried them, more than anywhere in Europe and a quarter of the European total, according to the Centre for Social Justice (CSJ), a thinktank. The report also found some websites selling class A drugs such as heroin and crack cocaine for postal delivery. Elsewhere, the report criticises the government's inadequate response to heroin addiction, revealing that more than 40,000 drug addicts in England have been on substitutes such as methadone for at least four years.

The CSJ, which was set up by Iain Duncan Smith, the work and pensions secretary, also claims the response to the growing crisis of legal highs, or new psychoactive substances, is bureaucratic and inadequate. Since 2010 the government has used temporary banning orders three times to control approximately 15 substances. In the same period, more than 150 new substances have emerged and are widely available online and in high street shops.

Among those aged 15-24 in Britain, at least 670,000 admit they have taken legal highs. In England, 6,486 people were treated in 2011-12 for abusing legal highs, an increase of 39% compared with five years previously. In addition, 43 young people died in 2010 as a result of taking now outlawed methcathinones – an eightfold increase on the previous year.

Unless action is taken, warns the report, the number of young people taking these drugs will continue to rise.

It also attacks a failure to offer heroin addicts effective treatment and through new freedom of information data reveals that 55% of councils in England have cut funding for residential treatment since the coalition government took power.

Christian Guy, director of the CSJ, said: "While our addiction problem damages the economy, it is the human consequences that present the real tragedy. Drug and alcohol abuse fuels poverty and deprivation, leading to family breakdown and child neglect, homelessness, crime, debt and long-term worklessness.

"Dependency destroys lives, wrecks families and blights communities."

Almost a third of the people in England in substitute prescribing treatment, usually methadone, have been on it for four years or more with one in 25 on a continuous substitute prescription programme for more than a decade – a 40% rise since the coalition took office.

Guy said: "Methadone can be a way of stabilising chaotic drug users, but we found evidence that it is being used to keep a lid on problems. Large numbers of addicts are stranded on this state-supplied substitute and forgotten. This broken system is no different to taxpayers supporting an alcoholic by prescribing them vodka instead of them drinking gin."

The report also warns that Britain is facing an epidemic of drink-related conditions with a quarter of adults in England drinking to harmful levels and one in 20 described as "dependent drinkers". Alcohol-related deaths have doubled since 1991 across the UK and liver disease is now one of the big five killers alongside heart and lung disease, strokes and cancer.

The report found that alcohol abuse was not spread evenly across the UK. "The north-south divide is stark," says the report, called No Quick Fix. Of the 30 local authorities with the highest rate of alcohol-related admissions, 26 are in the north.

Noreen Oliver, chairwoman of the CSJ review, said: "Despite some slow progress in this last three years, much more needs to be done to tackle the root causes of addiction so that people have a better chance of breaking free."

The UK also has the highest rate of opiate addiction in Europe and the highest lifetime-use of amphetamines, cocaine and ecstasy. Alcohol dependence among British men is second in western Europe and seventh overall. Among women, alcohol dependence is higher in Britain than anywhere in Europe.