Ministers wait for report on legal high drugs before taking 'immediate action'

Ms Harman said such "changing chemical substances" were "extremely dangerous" and should be avoided at all costs.

The deaths of Louis Wainwright, 18, and Nicholas Smith, 19, on Monday following a night out in the Scunthorpe area have provoked a nationwide debate about so-called legal high drugs.

It also emerged yesterday that a 46-year-old man in East Sussex died from mephedrone poisoning. John Sterling Smith suffered a heart attack at his home in the early hours of February 7.

During Commons exchanges on forthcoming business, the Tories said such narcotics should be banned temporarily until a "proper assessment" of their risks was carried out.

The Advisory Council on the Misuse of Drugs (ACMD) is to issue a report into a group of legal highs, including mephedrone – also known as "M-Cat" or "miaow miaow" – at the end of this month. The Government will then take "immediate action" based on the advice.

Shadow Commons leader Sir George Young said: "The tragic death of the two young boys who took mephedrone has heightened the need to react more quickly to the ease with which existing narcotics can be reconstituted to form legal substances.

"Do you agree with our view that we should be able to ban these drugs temporarily until there is a proper assessment of the risks they present and then ban permanently those that are dangerous?"

Ms Harman replied: "I think that the House will be aware that there are changing chemical substances which are being manufactured and they are extremely dangerous and young people ought to be aware that they should not be taking these substances; they could put their health and even their lives at stake.

"Obviously the Government is able to draw on the important scientific advice of these changing chemical compounds from the ACMD.

"But the most important thing right now is for young people to have that important warning – that they should not be taking these substances because they are extremely dangerous."

Three males, aged 26, 20 and 17, arrested in connection with the deaths of the teenagers have been released on bail pending further inquiries.

A fourth man also arrested in the investigation remains in custody.

Humberside Police said all four were detained on suspicion of supplying a controlled drug.

A spokesman also said post-mortem examinations on Mr Wainwright and Mr Smith have been completed but the results of toxicology tests may not be known for several weeks.

He said: "Humberside Police is continuing to encourage anyone who knows somebody who has possession of the drug to either hand it in to a local police station or dispose of the substance as soon as possible and contact Humberside Police."