Almost a quarter of street drugs are not what users think they are, some being far more powerful and dangerous than expected, according to findings from the UK’s first community-based drug-checking service.

The testing, carried out in Bristol and Durham, involved more than 170 substances of concern being submitted and analysed by a team of chemists in a pop-up lab, with follow-up healthcare consultations delivered to more than 200 users.

Nearly one in four of the drugs sold (24%) were not what they purported to be, according to the results, published this week in the British Journal of Clinical Pharmacology. Drugs sold as MDMA or ecstasy turned out to be n-ethylpentylone, which has been linked to overdose deaths, while a substance purporting to be ketamine was found to be a new psychoactive substance with the chemical name 2-FDCK, a synthetic drug that is about one-and-a-half times more powerful and whose effects lasts for up to three times as long as ketamine.

A small number of submitted samples were associated with “problem drug-use”, including heroin containing paracetemol and caffeine, and a synthetic version of cannabis.

“The core problem is supply and demand,” said Prof Fiona Measham, chair in criminology at the University of Liverpool, and director of harm reduction charity The Loop, which conducted the tests.

“As demand for drugs is as buoyant as ever, we see increasingly innovative attempts to meet that demand, with drug users vulnerable to the sophisticated operations of organised crime. Testing bypasses the central problem here, which is that users cannot be sure what they’ve bought in terms of content or strength.”

As a result of the testing, which took place in several venues, including a church, The Loop was able to warn users about problem drugs in circulation via social media.

“Identifying a ketamine analogue for the first time in a small city like Durham, with several of the dealers having missold it as ketamine, illustrates both the extent to which new psychoactive substances are being missold as established drugs on the streets of Britain and also how street dealers themselves can be vulnerable to misselling by suppliers higher up the chain,” Measham said.

“Some of the users had already tried the substance and knew something wasn’t quite right with it but didn’t know what. None of us – the students, the dealers or the testing team – expected it to be this new ketamine analogue though. It makes me wonder what else is in circulation that could be causing harm to people all across the UK.”

Drug-related deaths in Britain are at record levels, with the most recent official figures showing that 2,917 deaths from illicit drugs were recorded in England and Wales in 2018, an annual rise of 17% .

Drug-safety testing originated in California in the 1960s and spread across Europe in the late 1980s. Both the Swiss and New Zealand governments are funding national evaluations, with a Europe-wide evaluation also planned.

“One of the distinct values of drug-safety testing is that we ask people what they think they have bought then test it and find out what they have actually bought,” Measham said. “In this way we are gradually building a much better understanding of how illegal drug markets operate in the UK, including the extent of misselling and adulteration in markets. For example, we now know that festival dealers are twice as likely to missell substances as neighbourhood dealers, through our festival testing. Community-based testing like these pilots allows us to get a better understanding of that misselling within different city centre drug-markets too. This can then alert drug-users and emergency services in the short term and also inform healthcare services in the long term.”Three in 10 drug users intend to take smaller doses in future after receiving the results of the drug testing and speaking to a healthcare professional; a third will be more careful about polydrug use; and one in 10 will dispose of further substances in their possession.

Steve Rolles, of the Transform Drug Policy Foundation, said: “As drug-related deaths reach new records, it’s clear that putting our heads in the sand and wishing the problem would go away isn’t good enough. We know that drug-safety testing works. It’s time the government showed some long-absent leadership and got fully behind it.”

• This article was amended on 21 February 2020 to clarify that the 17% figure for illicit drug deaths was an annual increase.