Image caption The report said drug prices had fallen in real terms over 20 years, while purity had increased

Illegal drugs are now cheaper and purer globally than at any time over the last 20 years, a report has warned.

The International Centre for Science in Drug Policy said its report suggested the war on drugs had failed.

The report, published in the British Medical Journal Open, looked at data from seven international government-funded drug surveillance systems.

Its researchers said it was time to consider drug use a public health issue rather than a criminal justice issue.

The seven drug surveillance systems the study looked at had at least 10 years of information on the price and purity of cannabis, cocaine and opiates, including heroin.

The report said street prices of drugs had fallen in real terms between 1990 and 2010, while their purity and potency had increased.

In Europe, for example, the average price of opiates and cocaine, adjusted for inflation and purity, decreased by 74% and 51% respectively between 1990 and 2010, the Vancouver-based centre said.

The report also found there had been a substantial increase in most parts of the world in the amount of cocaine, heroin and cannabis seized by law enforcement agencies since 1990.

Most national drug control strategies have focused on law enforcement to curb supply despite calls to explore other approaches, such as decriminalisation and strict legal regulation, it said.

It concluded: "These findings suggest that expanding efforts at controlling the global illegal drug market through law enforcement are failing."

We desperately need to shift the regime from a prohibitionist one to one of legal regulation Transform Drug Policy Foundation

Co-author Dr Evan Wood, scientific chairman of the centre, said: "We should look to implement policies that place community health and safety at the forefront of our efforts, and consider drug use a public health issue rather than a criminal justice issue.

"With the recognition that efforts to reduce drug supply are unlikely to be successful, there is a clear need to scale up addiction treatment and other strategies that can effectively reduce drug-related harm."

The study comes two days after a senior UK police officer said class A drugs should be decriminalised.

On Sunday, Chief Constable Mike Barton, of Durham Police, said drug addicts should be "treated and cared for, not criminalised".

The chief constable, who is the intelligence lead for the Association of Chief Police Officers, told the Observer he believed decriminalisation would take away the income of dealers, destroy their power, and that a "controlled environment" would be a more successful way of tackling the issue.

He said prohibition had put billions of pounds into the hands of criminals and called for an open debate on the problems caused by drugs.

Mr Barton is among a small number of top police officers in the UK who have called for a major review of drugs policy.

'Tackle organised crime'

Danny Kushlick, of the Transform Drug Policy Foundation, welcomed Mr Barton's comments and said prohibition of drugs had been a "miserable failure".

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"We desperately need to shift the regime from a prohibitionist one to one of legal regulation," he said.

He said criminalising drugs had "gifted one of the largest commodity trades on earth to organised crime".

"It's an absolute no brainer for any government that is thinking responsibly about how best to regulate these things that they look after them and don't leave it in the hands of criminals," Mr Kushlick added.

The Home Office said drugs were illegal because they were dangerous.

It said the UK's approach on drugs was clear: "We must help individuals who are dependent by treatment, while ensuring law enforcement protects society by stopping the supply and tackling the organised crime that is associated with the drugs trade."

No major UK political party supports decriminalisation of class A drugs, though the Liberal Democrats said Britain's current approach was "costly and ineffective".

A Lib Dem spokeswoman said the government should consider other approaches used overseas and should "always base drugs policy on independent scientific advice", but did not say the party would decriminalise any currently banned drugs.

Labour said it would not decriminalise any banned recreational drugs, while the Green Party wants to make cannabis legal.