Seventy-eight consumption room facilities are in operation across seven EU countries, as well as Canada and Australia, and while the Home Office backs heroin assisted treatment it has opposed consumption rooms in the UK.

Home Office minister, Victoria Atkins, in a Westminster debate last month, said: “We have no intention of introducing drug consumption rooms,” and claimed they were not always evidence backed.

This followed efforts, by council and health chiefs in Scotland, to establish a consumption room for heroin users in Glasgow, which is currently prevented because of the risk of legal prosecution of staff.

But an evaluation of the supervised injection site “Insite” scheme in Vancouver, Canada – seen by The Independent – found it cut overdoses by 35 per cent, increased uptake of detoxification services by users, and saved more than $17m (£10.12m) by reducing new HIV infections.

It led to fewer cases of drugs consumers injecting in public spaces, and less spending on needle clear ups.

It was also not shown to increase the numbers of heroin users or crime in the area – with vehicle break-ins falling.

Canadian health chiefs involved with the scheme wrote to Ms Atkins following her suggestion that it was not evidence backed, saying her arguments were “neither factually nor legally accurate”.

In a letter seen by The Independent, they added: “We invite you and your colleagues to visit Vancouver, tour Insite and other harm reduction facilities in the city (and elsewhere in the country), and see for yourself how such facilities operate.”

Richard Elliott, one of the signatories and executive director of the Canadian HIV/Aids Legal Network, told The Independent that they too had struggled to introduce the first drug consumption rooms.

“They were a hard sell in Canada, dating back to the late 1990s, but lots of advocacy by people who use drugs, human rights advocates, public health people, some enlightened municipal people in Vancouver, eventually broke through – and significantly, this was against the unfortunate backdrop of the last major overdose crisis,” he said.

However, protests, legal action and “backsliding” under the previous Conservative federal Government have shown that progress can be wiped out.

“We’re in a very different place now when it comes to harm reduction, including drug consumption rooms – but nothing can be taken for granted,” Mr Elliott said.

“What appears to be happening in the UK now is reminiscent of what has happened over the last 20 years in Canada.”

In Scotland, the Glasgow Health and Social Care Partnership is continuing to push for a treatment room site. A spokesperson said: “Discussions are ongoing on how we can best secure the legislative framework needed to ensure the facility can open legitimately.

“With HIV infection still rising among drug injectors and drug-related deaths a persistent issue for the city, the case for the facility in Glasgow remains as compelling as ever.”