Drugs experts have warned that new legal highs are flooding the market following the ban on meow.

Speaking at the inquest of a Hove man who died after taking the second-largest known dose of mephedrone, known as meow, an expert forensic toxicologist warned the law was “constantly playing catch-up” with drug makers.

Police and drugs campaigners echoed the warning about the surge of new drugs.

Jenny Button, head of the toxicology service at St George’s University, London, said: “Through clever chemistry an illegal drug can be changed into a legal one.

“It is going to be a case of constantly playing catch-up.

“We have already now started to see new designer drugs as a result of the classification of meow.

“Users are being subjected to more and more substances.”

Ms Button, whose department tests unclassified drugs which cannot be detected by the Forensic Science Service, said that John Smith, 46, of The Drive, Hove, had 1.3mg of mephedrone per litre of his blood after he died on February 7.

She said levels of meow ranging from 0.05mg to 1.7mg had been found in postmortem examinations but the highest toxicity found in someone alive was 0.1mg.

Police found another unclassified substance – BK-NBDB, also known as Doves – at Mr Smith’s home.

Ms Button said: “We know even less about this drug than we do about mephedrone.

This one has started to appear on the market since the classification.”

Mr Smith injected mephedrone three or four times in the five hours leading up to his death, but had not taken any other drugs or drunk alcohol.

Friends Christopher Sarson and Ian Turner, who had taken the drug with him, said he suddenly collapsed clutching his chest about half an hour after taking his final hit.

Pathologist David Wright found that Mr Smith had suffered coronary artery disease as well as mephedrone poisoning, but said: “It seems unlikely he would have died when he did without mephedrone.”

Assistant deputy coroner Karen Henderson said: “We know he took mephedrone.

“We also know he injected it, which is an unusual way of taking it to get a bigger high.

“Meow was a legal high and we have heard about the ingenious ways to try to escape the drugs laws, which doesn’t bode well for the future.

“It is absolutely clear the contribution of mephedrone was significant and being legal does not mean safe.

“It is my wish that their destructive nature is made clear.”

Ms Henderson recorded a narrative verdict that Mr Smith died as a result of mephedrone poisoning with a background of coronary heart disease.

Drugs campaigner Maryon Stewart, whose daughter Hester died after taking the then legal high GBL, said last night that she hoped for tougher Government action on new drugs.

She said: “There are about 400 of these legal highs waiting to come on to the market.

“We have got to be able to give people some direction about what’s safe and what’s potentially harmful.”

Detective Inspector Bill Warner, of Sussex Police, said: “Undoubtedly we will see changes to the molecular structure to drugs to create legal highs.

“We are dealing with big money and big money attracts some very intelligent people who will do whatever it takes to get around the law.

“Unfortunately even education of the dangers won’t stop all people from trying drugs.”