Traffickers are marketing "legal alternatives" to ecstasy, which is posing a huge challenge to the conventional methods of drug control, according to the European drug agency.

Suppliers, keen to exploit grey areas within national laws, are using a different chemical compound to make ecstasy - mCPP as opposed to MDMA - which is not banned in several member states.

Paul Griffiths, a scientific coordinator with the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), explained ecstasy was simply the street name; what made it illegal was the compound it contained - MDMA or any of its analogues.

"There is a growing sophistication to marketing legal alternatives to illicit drugs, which represents a worrying development," he said.

This statement comes just days after Steve Marsden, the 50-year-old Briton jailed for 25 years for conspiring to traffic 50,000 ecstasy pills, walked out of prison a free man after he was acquitted by an appeals court.

Mr Marsden's case clearly highlights the problems posed for enforcement agencies. He was released because the pills - hidden behind the panels of his Mitsubishi Pajero as he was driving from Sicily to Malta in 2006 - contained mCPP, which was not banned in Malta.

Mr Marsden, who spent three-and-a-half years behind bars, left prison on Monday night and is planning to institute a civil case against Malta for compensation and lost time.

Mr Griffiths said some member states had implemented measures against ecstasy pills containing mCPP. Malta is one of them.

He pointed out that, since mCPP was a legitimate ingredient used in pharmaceutical drugs, such as antidepressants, it made it harder to ban its use.

These challenges emerged yesterday during the annual presentation of the EMCDDA report in Brussels on the state of the drugs problem in Europe.

The EU early warning system has been monitoring mCPP since 2005 but this year it has seen a huge influx of this recreational drug - up to half of all the tablets analysed - in countries such as Denmark and the Netherlands.

According to the report, in 2008, mCPP continued to be the most widely available new synthetic drug on the market, encountered alone or in combination with MDMA.

Popping a pill containing mCPP is not more dangerous than one with the traditional ingredient MDMA but it affects people differently and can cause nausea and vomiting. Party-goers seeking a euphoric high require a bigger dose, which puts them at risk if they have no clue what they are consuming.

Mr Griffiths conceded suppliers were moving at a more rapid pace than politicians and it was crucial to focus on testing the legal alternatives and their health implications.

EMCDDA director Wolfgang Götz said these developments challenged existing policies and practice and insisted the trend to replace MDMA with mCPP in ecstasy pills was being closely followed.

"This reality not only leads to more negative outcome but also challenges services as they have to respond to a more complex set of needs... " he said.

This concern was echoed by Carel Edwards, head of the European Commission's anti-drug coordinating unit, who admitted the EU's response had not been "particularly adequate" against the fast and sophisticated illicit market.

"Despite having Europol and Eurojust, the typical response against trafficking remains stubbornly national overall. As long as we remain 27 separate countries against a single global market, we will never get to the bottom of this problem," he warned.

How drugs are made illegal

The authorities are informed of any new dangerous drugs that emerge on the international scene through a well-developed network of international contacts.

These drugs are then added to the schedule of outlawed drugs as swiftly as possible to enable the Maltese law enforcement agencies to effectively control them long before anyone tries to import them.

"The chemical compound mCPP, which was the subject of the Marsden case, was a brand new drug that had only been identified in three other European countries before it was intercepted in Malta on July 9, 2006," a spokesman for the Justice Ministry said.

This was the reason why the compound had not yet been included in the schedule. It was now a controlled substance, the ministry said.

Meanwhile, the police have confirmed that "there have been cases" where traffickers could not be prosecuted because the drugs intercepted were legal.

"This is due to the fact that, upon forensic examination of the substance seized, whether in tablet, powder or any other form, it was established that the active ingredient contained was not a scheduled one. This, along with the evidence in hand, did not constitute an offence."

There have been cases, for example, where pills intended to be sold as ecstasy actually contained a substance such as caffeine instead of MDMA. The pills have the same external appearance and their effect is usually similar. The seller, his supplier and the end buyer are usually unaware that the substance contained is not illegal.