New "legal highs" are being discovered at the rate of one a week, outstripping attempts to control their availability and exposing what some experts claim is the "ridiculous and irrational" government policy of prohibition.

Officials monitoring the European drugs market identified 20 new synthetic psychoactive substances in the first four months of this year, according to Paolo Deluca, co-principal investigator at the Psychonaut Research Project, an EU-funded organisation based at King's College London, which studies trends in drug use. He said officials at the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), an early-warning unit, had detected 20 new substances for sale by May this year. In 2010 the agency had noted 41 new psychoactive substances, a record number, many of which were synthetic cathinone derivatives that can imitate the effects of cocaine, ecstasy or amphetamines.

Deluca said that, given the plethora of new substances, the government's attempts to ban legal highs is not a "feasible" solution. "It's also becoming very difficult to know exactly how many new compounds there are, because you have all these brand names and when you test the batch they are different from the following one." The UK, according to his reasearch, remains Europe's largest market for legal highs and synthetic compounds.

Campaigners at the Transform Drugs Policy Foundation (TDPF), a charity, said the unprecedented speed at which new drugs are appearing highlights the government's "unsustainable" strategy of banning each one, as well as a basic lack of understanding of how the drugs market functions.

Last year the government unveiled plans to introduce temporary 12-month bans on "legal highs", while the Advisory Council on the Misuse of Drugs considered a possible permanent ban. So far two substances have received a complete ban – mephedrone, the former legal high known as "meow meow", and naphyrone, otherwise known as "NRG1". Another two, phenazepam and Ivory Wave, have also received an import ban, which means the UK Border Agency can seize and destroy shipments following safety concerns.

The government's continued emphasis on banning illegal compounds flies in the face of growing calls for a fresh approach to tackling drugs. Earlier this year prominent public figures, including former heads of MI5 and the Crown Prosecution Service, said the "war on drugs" had failed and should be abandoned in favour of evidence-based policies that treat addiction as a health problem and avoid criminalising users.

Steve Rolles, senior policy analyst at TDPF, said attempts to ban one new substance after another was "like a cat chasing its tail". He added: "Each time they ban one, another emerges. It seems to show a blindness to the basic market dynamic, effectively creating a void for backstreet chemists to create another product." The group is one of many urging the government to adopt a regulatory position between total prohibition or an "internet-free-for all".

Deluca cites the case of mephedrone, which despite being banned last year remains as popular as cocaine among teenagers and young adults, according to official figures released in July. Home Office data from the British Crime Survey estimate that around 300,000 16- to 24-year-olds used mephedrone in the previous 12 months, a similar level of popularity to the use of cocaine among the same age bracket. Deluca added: "The legality of the compounds will not stop potential users, only the quality."

The EMCDDA favours generic bans that would cover entire groups of structurally related synthetic compounds, or chemical families, therefore removing the need to ban individual substances as they appear on the market. Deluca said: "It is impossible to implement a ban for every single new compound."

Rolles said legal highs should be investigated and regulated using the same model as conventional pharmaceuticals. "It's just ridiculous, irrational really. If you're not looking at the regulatory options, then you're not following an evidence-based approach – you are following a political mandate."