More than 13,000 heroin and opioid deaths have been missed off official statistics in England and Wales, raising concerns about the impact on the government’s approach to tackling addiction.

Research from King’s College London, shared exclusively with BBC News, found that there were 39,232 opioid-related deaths between 2011 and 2022, more than 50% higher than previously known.

The error has been blamed on the government’s official statistics body not having access to correct data and it is understood ministers are now working with coroners to improve the reporting of deaths.

A former senior civil servant said fewer people might have died if drug policies had been based on accurate statistics.

The number of opioid deaths per million people in England and Wales has almost doubled since 2012, but this new study means the scale of the problem is likely to be even greater.

Researchers from the National Programme on Substance Use Mortality at King’s used data from coroners’ reports to calculate a more accurate estimate of opioid-related deaths.

Opioids include drugs such as heroin that come from the opium poppy plant, as well as synthetically-made substances like fentanyl.

The Liberal Democrats have said the government needs to “urgently investigate” how the error was made.

The reliability of the Office for National Statistics (ONS) data relies on coroners naming specific substances on death certificates, something which often does not happen.

Specific substances such as heroin are instead sometimes only included on more detailed post-mortem reports or toxicology results, which the ONS does not have access to.

Government data on overall drug deaths, which does not name specific substances, is not affected by the error, but ministers’ decision-making is generally influenced by the more granular statistics.

The body that oversees police commissioners says correct data on opioid deaths could have led to more funding and better treatment for front-line services such as police forces and public health.

Sir Philip Rutnam, who was the most senior civil servant at the Home Office between 2017 and 2020, told the BBC it was “quite possible” that fewer people would have died, if the government’s drug policies had been based on accurate statistics.

He told BBC Radio 4’s PM programme: “It really does matter, first of all the level of attention given to these issues, but then specifically it will affect decisions on how much funding to put into health-related programmes, treatment programmes, or into different bits of the criminal justice system.”

Ben was 27 when he died from a heroin overdose in 2018, but his death was ruled as “misadventure” and was never included on the official opioid death statistics.

His addiction began with cannabis when he was a teenager and progressed to using aerosols and eventually heroin.

“Ben was just a very kind person. We miss him, we all miss him every day,” said his mother Hilary.

At one point, she said Ben appeared to “turn a corner”.

He was awarded a place in a rehab facility, but shortly before he was set to move in, Hilary got the phone call she had always dreaded.

“I think what happened is, he wasn’t using,” she said. “They think probably about three months and his tolerance had gone down.”

Ben’s family believe that different treatment and support for drug addicts could have helped him.

Dr Caroline Copeland, who led the new research, said drug policies “will not have the desired impact unless the true scale of the problem is known”.

She added: “We need to alert coroners to the impact that not naming specific drugs as the cause of death has on the planning and funding of public health policies.”

The research, which has been peer-reviewed and published in the International Journal of Drug Policy, focused specifically on opioid deaths, but similar undercounts are thought to exist in data about deaths from other drugs too.

Further work by King’s College London has found that 2,482 cocaine-related deaths have also been missed off ONS statistics over the last 10 years.

David Sidwick, the drugs lead for the National Association of Police and Crime Commissioners, told the BBC the organisation would “be pushing hard” for more treatment funding, in light of the faulty statistics.

Mr Sidwick, who is also a Conservative police and crime commissioner, said more accurate data would lead to “better decisions about the amount of funding required for treatment” and suggested “new treatment methods” such as buprenorphine, a monthly injection that can help heroin users overcome addiction.

Helen Morgan, the Liberal Democrat health spokesperson, said: “I dread to think of the lives that may have been lost due to damaging policies based on faulty stats.”

She added: “The government now needs to step up, launch an investigation and ensure that the ONS is given access to the data it needs so that it can never make this error again.”

The ONS, which helped with the research, said it had warned that “the information provided by coroners on death registrations can lack detail” on the specific drugs involved.

A spokesperson added: “The more detail coroners can provide about specific drugs relevant to a death will help further improve these statistics to inform the UK government’s drug strategy.”

The flaw in the ONS system is not present in Scotland, where there are no coroners and where National Records Scotland (NRS) is responsible for collating official statistics.

Unlike the ONS, the NRS does receive more detailed pathology reports, but differences in how deaths are reported across the UK make it difficult to compare.

The opioid undercounting raises further questions about the under-fire ONS, which has been accused of failing on several statistical fronts recently.

Data sets on job markets and immigration have been criticised and earlier this year a government review said the ONS had “deep-seated” issues which needed tackling.

A spokesperson for the Department of Health and Social Care said: “We continue to work with partners across health, policing and wider public services to drive down drug use, ensure more people receive timely treatment and support, and make our streets and communities safer.”