A blanket ban on legal highs due to come into force this week will lead to more deaths and only benefit drug dealers and politicians, critics have claimed.

The substances, which mimic the effects of already banned drugs, are being outlawed on Thursday due to concerns their potency is fuelling health problems and anti-social behaviour.

But critics have said that the law will simply force users, who are often among the most vulnerable in society, to turn to street dealers and the criminal underworld, leading to more drug-related deaths.

Professor David Nutt, the former Government drugs tsar, told The Independent: “It is a completely nonsense piece of legislation. It is purely politics.

“The only people who will benefit will be the drug dealers. They’ll have a monopoly.”

The popularity of legal highs has increased dramatically in recent years. In 2013, according to the United Nations’ World Drug Report, 670,000 British 15- to 24-year-olds had tried legal highs at least once. The death toll rose from 10 legal high-related deaths in England and Northern Ireland in 2009 to 68 in 2012.

Often compared to cannabis, the potency and addictiveness of legal highs can vary significantly. In a special report for The Independent, some users in Newcastle spoke of the substance as having the “effect of heroin”.

Legal Highs in Newcastle

In fact, heroin addicts who switched to legal highs as a cheaper alternative have been known to return to the Class A drug in the belief it is less damaging.

The Government has claimed that by imposing prison sentences of up to seven years on those making or supplying drugs capable of producing a psychoactive effect, the new law will clearly signal the dangers of legal highs, which have been sold in head shops, convenience stores and online.

Harry Shapiro, the chief executive of the drugs information charity DrugWise, said the new law will make legal highs harder to obtain, but warned: “The problem will almost certainly be that legal highs will just become street drugs.

“The same people selling heroin and crack will simply add this to their repertoire.”

He added: “Politically, they [legal highs] are low-hanging fruit. The easiest thing for any Government to do is to stop people buying these things from shops next to Mothercare, but don’t imagine that is going to solve the problem.”

Prof Nutt said that while some head shops have exercised quality control and showed a degree of responsibility towards users, street dealers would be totally unscrupulous. He claimed that they would use the internet to source legal highs made in India and China, with no regard for quality, and would aim to get legal high users on to heroin and crack.

“It will be a scary market,” he said. “And there will be much less safety. Deaths will increase.

“There will be no quality control – people won’t stop using legal highs, they will just use more dangerous ones.

World's 10 deadliest street drugs Show all 10 1 /10 World's 10 deadliest street drugs World's 10 deadliest street drugs Whoonga Whoonga is a combination of antiretroviral drugs, used to treat HIV, and various cutting agents such as detergents and poisons. The drug is widely available in South Africa due to South Africa’s high rate of HIV sufferers, and is believed to be popular due to how cheap it is when compared to prescribed antiretrovirals. The drug is highly addictive and can cause major health issues such as internal bleeding, stomach ulcers and ultimately death Getty World's 10 deadliest street drugs Scopolamine Scopolamine is a derivative from the nightshade plant found in the Northern Indian region of South America (Ecuador, Colombia and Venezuela). It is generally found in a refined powder form, but can also be found as a tea. The drug is more often used by criminals due its high toxicity level (one gram is believed to be able to kill up to 20 people) making it a strong poison. However, it is also believed that the drug is blown into the faces of unexpecting victims, later causing them to lose all sense of self-control and becoming incapable of forming memories during the time they are under the influence of the drug. This tactic has reportedly been used by gangs in Colombia where there have been reports of people using scopolamine as way to convince victims to rob their own homes World's 10 deadliest street drugs Heroin Founded in 1874 by C. R. Alder Wright, heroin is one of the world’s oldest drugs. Originally it was prescribed as a strong painkiller used to treat chronic pain and physical trauma. However in 1971 it was made illegal under the Misuse of Drugs Act. Since then it has become one of the most destructive substances in the world, tearing apart communities and destroying families. The side effects of heroin include inflammation of the gums, cold sweats, a weak immune system, muscular weakness and insomnia. It can also damage blood vessels which can later cause gangrene if left untreated World's 10 deadliest street drugs Crack cocaine Crack cocaine first came about in the 1980’s when cocaine became a widespread commodity within the drug trafficking world. Originally cocaine would have attracted a high price tag due to its rarity and difficulty to produce, but once it became more widespread the price dropped significantly. This resulted in drug dealers forming their cocaine into rock like shapes by using baking soda as a way of distilling the powder down into rock form. People were doing this because it allowed for them to sell cocaine at a lower quantity and to a higher number of people. The side effects of crack cocaine include liver, kidney and lung damage, as well as permanent damage to blood vessels, which can often lead to heart attacks, strokes, and ultimately death World's 10 deadliest street drugs Crystal meth Not just famous because of a certain Walter H White, but also because it is one of the most destructive drugs in the world. First developed in 1887, it became widely used during the Second World War when both sides would give it to their troops to keep them awake. It is also believed that the Japanese gave it to their Kamikaze pilots before their suicide missions. After the war crystal meth was prescribed as a diet aid and remained legal until the 1970s. Since then it has fallen into the hands of Mexican gangs and has become a worldwide phenomenon, spreading throughout Europe and Asia. The effects of crystal meth are devastating. In the short-term users will become sleep depraved and anxious, and in the long-term it will cause their flesh to sink, as well as brain damage and damage of the blood vessels World's 10 deadliest street drugs AH-7921 AH-7921 is a synthetic opioid that was previously available to legally purchase online from vendors until it became a Class A in January 2015. The drug is believed to have 80% of the potency of morphine, and became known as the ‘legal heroin’. While there has only been one death related to AH-7921 in the UK, it is believed to be highly dangerous and capable of causing respiratory arrest and gangrene World's 10 deadliest street drugs Flakka Flakka is a stimulant with a similar chemical make-up to the amphetamine-like drug found in bath salts. While the drug was originally marketed as a legal high alternative to ecstasy, the effects are significantly different. The user will feel an elevated heart rate, enhanced emotions, and, if enough is digested, strong hallucinations. The drug can cause permanent psychological damage due to it affecting the mood regulating neurons that keep the mind’s serotonin and dopamine in check, as well as possibly causing heart failure World's 10 deadliest street drugs Bath salts Bath salts are a synthetic crystalline drug that is prevalent in the US. While they may sound harmless, they certainly aren’t the sort of salts you drop into a warm bath when having a relaxing night in, they are most similar to mephedrone, and have recently been featured throughout social media due to the ‘zombification’ of its. The name comes from the fact that the drug was originally sold online, and widely disguised as bath salts. The side effects include unusual psychiatric behaviour, psychosis, panic attacks and violent behaviour, as well as the possibility of a heart attack and an elevated body temperature World's 10 deadliest street drugs Purple Drank One of the more unusual drugs around at the moment, purple drank was popularised in 90s hip hop culture, with the likes of Jay Z and Big Moe all mentioning it in their songs. It is a concoction of soda water, sweets and cold medicine, and is drunk due to cold medicines high codeine content, which gives the user a woozy feeling. However it can also cause respiratory issues and heart failure World's 10 deadliest street drugs Krokodil Krokodil is Russia’s secret addiction. It is believed that over one million Russians are addicted to the drug. Users of krokodil are attracted to the drug due to its low price; it is sold at £20 a gram while heroin is sold for £60. However, krokodil is considered more dangerous than heroin because it is often homemade, with ingredients including painkillers, iodine, lighter fluid and industrial cleaning agents. This chemical make-up makes the drug highly dangerous and likely to cause gangrene, and eventually rotting of the flesh

“And street dealers want to get you on heroin and crack, because they are more addictive. More people will be dying from more dangerous drugs.”

The effects of the UK law, he added, would mirror those seen in Ireland, which banned legal highs in 2010.

“There was a transient reduction in use,” he said. “But now usage has gone back to where it was before, if not higher. Deaths have gone up.”

In December, Ireland’s National Drug-Related Deaths Index showed drug poisoning deaths involving legal highs increased from six in 2010 to 28 in 2013.

The European Commission has said that between 2011 and 2014, Ireland experienced Europe’s second largest increase in legal high use among 15- to 24-year-olds. One Irish user told the BBC that after the ban closed head shops: “People started selling it on every street. It was even easier to get.”

Footage of some of the people in Newcastle city centre under the influence of legal highs

Critics have also pointed to the fact that drug makers have allegedly proved adept at producing slightly different new substances so quickly that it has been hard for scientists and the law to keep up.

A spokesman for the Irish Justice Department insisted the legislation was enforceable, and that one study had shown a drop in legal high use immediately after the ban was introduced, but acknowledged: “The emergence of new psychoactive substances happens at a pace that presents a challenge in the context of law enforcement [and] for the scientific and health authorities.”

Karen Bradley, the UK Home Office Minister for Preventing Abuse, Exploitation and Crime, said: “We owe it to all those who have lost loved ones to do everything we can to eradicate this abhorrent trade.

“This Act will end the open sale on our high streets and deliver new powers for law enforcement to tackle this issue at every level in communities, at our borders, on UK websites and in prisons.

“Allowing these substances to remain legal would not prevent crime committed by the illicit trade; nor would it address the harms associated with drug dependence.