An “unprecedented” spike in the number of deaths of homeless people in Glasgow has been linked to illegal versions of prescription tranquillisers that have flooded the market in Scotland over the past year.

Early data collected by addiction services indicates a 43% rise in the number of people who died of drugs overdoses in the city from January to October last year, compared with the same period in 2017.

There have been nearly 20 deaths in council-run homeless accommodation since the beginning of December, which frontline workers believe are related to the use of these street drugs, which have emerged across the UK.

As a sign of the severity of the problem, the police, health services and the council have issued a joint warning about so-called street Valium, also known as “street blues”, which is sold cheaply and in dangerously unpredictable concentrations.

In August, the Guardian reported on concerns about the rise in prescription drug use across the UK, sourced from the internet or other illegal suppliers, after Scottish government data showed a dramatic increase in the number of deaths linked to the tranquilliser Xanax.

Saket Priyadarshi, an associate medical director of NHS Greater Glasgow and Clyde addiction services, said: “I don’t think anywhere in England is experiencing the same level of harm with these new benzodiazepines as we are in the west of Scotland.

“I have been very concerned about the use of street blues for some time now. When people buy street blues, they do not know what is in the pills. The quality and dosage can be very variable. People might think they are taking diazepam, but it may be other much more potent benzodiazepines such as etizolam.

“The use of this drug in particular is associated with severe harm, from non-fatal overdoses and presentations to emergency departments, to fatalities. It is particularly dangerous when used in combination with other drugs like heroin and even prescribed methadone.”

Susanne Millar, the chair of Glasgow’s Alcohol and Drug Partnership, described the number of overdose deaths among people in settled homeless accommodation as “tragic” and unusual.

“Glasgow is currently experiencing an unprecedented number of fatal and non-fatal overdoses believed to be linked to the use of street Valium, although we won’t know conclusively until we have all the toxicology,” she said.

“People are dicing with death by taking this drug, particularly if it is mixed with alcohol and other drugs. Warnings have been issued to people by homelessness and addictions services, but sadly dealers are targeting the most vulnerable.”

Last month, a drugs gang was jailed for producing at least £1.6m of street Valium, using a pill press machine capable of producing 250,000 tablets an hour, from a garage in Paisley, a town to the west of Glasgow.

But local workers warned that while police have had some success in targeting the gangs manufacturing these pills, it appeared to have had little effect on their availability or price.

In October, addiction experts called for radical measures to tackle fatal drug overdosing in Scotland, as they predicted the number of drug-related deaths in 2018 was likely to exceed 1,000, the highest number recorded.