The “zombie plague” of spice users blighting UK cities has been caused by factors that were “utterly predictable” and exactly what critics of the legal highs ban warned about, the former drugs tsar has told The Independent.

Professor David Nutt said scenes in Manchester and other cities, with spice users likened in media reports to “walking zombies”, were proof that the ban introduced nearly a year ago was not working.

His criticism came as Manchester’s Crime Commissioner admitted to The Independent that it had become far harder for police to stop the sale of potentially deadly strains of spice because instead of simply talking to head shop owners, they had to disrupt criminal drug dealing operations.

Tony Lloyd also called on Home Secretary Amber Rudd to visit Manchester to see for herself how police, ambulance and health services were now “really stretched” by a spice problem that had grown far worse since the legal highs ban started.

“It’s exactly what I warned about,” said Prof Nutt, who is now professor of Neuropsychopharmacology at Imperial College, London. “The whole thing was utterly predictable. The trade has passed from the head shops to the street dealers – and on the black market people don’t care whether their ‘customers’ live or die.

“It is incredibly frustrating, but the Home Office and the Ministry of Justice have completely closed their minds to the reality of what is going on – and have done for a very long time.

“They think the only response is banning substances. It’s all heads in the sand, ‘drugs are bad, our policies are working’. They will never admit they got it wrong – but they have got it wrong.”

Prof Nutt was speaking after a reporter for the Manchester Evening News (MEN) described the Piccadilly Gardens area of the city as having been turned into “hell on earth” by “pale, wasted figures caught in a spice nightmare”.

Although spice, a synthetic cannabinoid, and other so-called ‘legal highs’ were banned by the Government under the Psychoactive Substances Act (PSA) in May 2016, the reporter described scenes of open “destitution” not seen in Manchester since the 1980s and 1990s.

As shoppers went about their daily business, users of spice – described by one addict as “like cannabis with the effect of heroin” - could be seen frozen in doorways, slumped on the floor, and in one case turning blue from the effects of a drug capable of inducing seizures and psychotic episodes.

Dozens of ambulances, the MEN reported, were being called to the area every day. Teenage pushers, the journalist wrote, were involved in “blatant drug dealing yards away from the children’s playground”.

With studies showing that 90 per cent of rough sleepers in Manchester city centre were using spice, one homelessness worker warned: “Things are reaching fever pitch … It’s a f***ing disaster zone.”

But in May, four days before the legal highs ban came into force, Prof Nutt had – with the backing of other critics – warned that the “nonsense legislation” would simply close the remaining head shops and force vulnerable addicts like homeless users into the arms of street dealers.

“The only people who will benefit,” Professor Nutt had told The Independent, “Will be the [street] drug dealers. They will have a monopoly.”

Now in what seems close to being an echo of that warning, Manchester city centre Inspector Phil Spurgeon has told the MEN: “I’m not being judgemental about the legislation, but the reality with the Psychoactive Substances Act is that it has shifted supply onto the streets.”

The senior police officer added: “The product was probably more consistent in the head shops. Now it’s more varied, the make-up is constantly changing.

“That’s why we’re seeing people collapsing, as the drug becomes more potent.”

This appeared similar to what Prof Nutt had warned about in May when he said: “It will be a scary market. There will be much less safety. There will be no quality control – people won’t stop using legal highs, they will just use more dangerous ones.

“Deaths will increase.”

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The fear of users dying has now been raised by Tony Lloyd, Greater Manchester’s interim mayor and its Police and Crime Commissioner, who admitted the legal highs ban had made it harder for police to intercept the most dangerous batches of spice – a drug whose precise chemical formula is constantly being tweaked by black market chemists, adding to the unpredictability of its effects.

He told The Independent: “There were those who warned that moving from a regulated supply to an unregulated one would have anarchic consequences.

“When spice was sold legally through shops, if there was a difficult batch coming through, causing extreme problems, it would be possible for police to deal with it via the shops. Now it is massively more complicated – the police have to launch an undercover operation [against criminals].”

Adding that some users had already experienced “very, very near death experiences, where they’ve essentially been dead and have been brought around,” Mr Lloyd said: “We should be very worried.”

He stopped short of an outright condemnation of the ban, but admitted that it was only since its introduction that Manchester had experienced such extreme problems.

He said: “I wasn’t aware of what we are now seeing until fairly recently – we are talking about post-ban, in recent weeks and months.

“But whether the upsurge could have happened anyway [without the ban], it’s difficult to say.”

Calling on Ms Rudd to visit Manchester to see for herself the true scale of the city’s spice problem, he added: “It would be a start for the Home Secretary to come up to Manchester to talk to those on the ground and get some proper view of the impact this is having on local resources.

“It’s not just the police. As much as anyone else, the ambulance and health services are being really stretched by the impact of spice.”

Nor is Manchester the only city where fears have been raised about how the legal highs ban has led to head shops being replaced by more ruthless criminal street dealers.

Legal Highs in Newcastle

In December, one user in Bradford, West Yorkshire, told The Independent that drugs like spice could now be ordered “like a takeaway”. Instead of having to travel to get their supplies from a head shop in a suburb three miles outside the city centre, users could just call up a delivery from one of the payphones which now had the numbers of criminal dealers carved into them.

In London, people working with homeless addicts were hearing of pushers offering cut-price deals where instead of selling by weight, they were dishing out spice according to however much money was in the homeless user’s pockets.

Such unscrupulous street dealer tactics, it was feared, would spread the use of the highly addictive drugs among the homeless and the vulnerable, who increasingly now include ex-prisoners who have become addicted after being exposed to widespread spice use in jail.

In Newcastle, one drugs worker said the ban had caused the city’s street dealers to raise the price of legal highs from £10 a gramme to £15 or £20. But that, he said, had just led to some homeless addicts committing more crime to fund their habit.

In other areas, including Blackpool, there have been reports of spice users looking like ‘zombies’ in popular city centre locations in broad daylight.

Prof Nutt, who was sacked by the Labour government in 2009 a day after claiming ecstasy and LSD were less harmful than alcohol and tobacco, said more useful steps might be decriminalising cannabis to steer people away from more harmful drugs, and adopting the Portugese decriminalisation model.

“In Portugal,” he said, “They have saved lives, saved money and prison space by decriminalising possession [in 2001] and treating it as a health issue. There, if you are caught with heroin, people talk to you about why you are taking it: addicts are treated, sent to dissuasion clinics.

“It works, but we would never do it, because that would be seen as ‘soft on drugs’.”

He added that instead, in December synthetic cannabinoids including spice were made class B drugs under the Misuse of Drugs Act 1971, meaning users could be punished with up to five years in prison for possession.

Previously, under the PSA, possession had only been punishable if the user was in prison. Outside of custodial institutions, the legal highs ban had targeted only suppliers.

Defending current policy, Sarah Newton, the Minister for Vulnerability, Safeguarding and Countering Extremism, said: “Drugs can devastate lives and communities; we will not tolerate them.

“That is why we passed the Act to outlaw so-called 'legal highs' and [later] introduced even tougher controls for synthetic cannabinoids.

"We are also tackling the harms caused by illegal drugs. Our Drug Strategy, to be published shortly, will build on the work already undertaken to prevent drug use in our communities and help dependent individuals, including homeless people and those in prisons.”

A Home Office spokesman added: “Almost 500 people were arrested in the first six months after the Psychoactive Substances Act came into force. In the same period 332 shops across the UK stopped selling the substances. Action by the National Crime Agency has also resulted in the removal of psychoactive substances being sold by UK based websites.