Drug campaigners have backed a warning from police chiefs that new Government powers to ban legal highs will not work.
The UK Drug Policy Commission (UKDPC), which analyses drug laws, said simply adding to the long list of substances already banned "won't make much difference".
Roger Howard, the UKDPC's chief executive, said: "We are deluding ourselves if we think that the temporary ban will solve the problem."
It comes after the Association of Chief Police Officers (Acpo) said the solution to tackling legal highs does not lie in "adding inexorably to the list of illicit substances". The police chiefs questioned "the extent to which legislation can realistically be used to address active choices being made by (predominantly young) people".
Mr Howard said: "It's right for the Government to react quickly when a worrying new drug emerges. But as Acpo have said, just adding the drug to the long list already controlled won't make much difference.
"The police and forensics are under too much pressure already to be able to offer much deterrent to potential users. We are deluding ourselves if we think that the temporary ban will solve the problem."
He went on: "We should think instead about what other powers we can use. Trading standards controls could provide a boosted first line of defence. We should encourage retailers to work with the authorities to reduce the damage that drug use can cause, and allow us to bring some discipline to an unregulated market."
Even the Government's own drugs advisers have concerns over the new powers, saying they hope a better way of tackling legal highs could be found.
Professor Les Iversen, chairman of the Advisory Council on the Misuse of Drugs (ACMD), said: "Picking them off one by one is not necessarily very productive." As one substance is banned, another one is produced which has similar effects but which is designed to avoid the scope of the ban, he said.
A Home Office spokeswoman said: "The UK is leading the way in cracking down on new psychoactive substances by banning them while the harms they cause are investigated. Drugs ruin lives and cause misery to families and communities. Our strategy is to keep drugs off the streets and punish the dealers."