A police investigation into hundreds of lives allegedly shortened by the wrongful administration of opioids at an NHS hospital has been expanded to include the review of 15,000 death certificates.

The 2018 report into the deaths of at least 456 elderly patients at Gosport War Memorial Hospital between 1989 and 2000 had found that despite patients not being sent to the NHS hospital for end-of-life care — often for rehabilitation or convalescence — they had been given powerful opioids intended to ease the pain of dying patients.

A former nurse at the hospital had claimed that “euthanasia was practised by the nursing staff”, an allegation that was reportedly also made by five other people.

Police launched an investigation into the hundreds of deaths in May 2019 and announced on Monday that the scope of the probe had widened to include the examination of 15,000 death certificates, according to The Times.

The Kent and Essex Serious Crime Directorate (SCD) is examining the allegedly wrongful deaths, between the widened timeframe of 1987 and 2001, under the code name Operation Magenta.

The SCD’s Deputy Assistant Commissioner Neil Jerome said: “The Operation Magenta team, which consists of both serving and retired detectives from a number of police forces across the country, in addition to other members of police staff… will soon total around 150 people.”

Deputy Assistant Commissioner Jerome confirmed that investigators were examining “millions of pages of documents, including more than 700 patient records, around 15,000 death certificates and… other seized materials”.

The report from 2018 found that there was “a disregard for human life and a culture of shortening the lives of a large number of patients” and an “institutionalised regime of prescribing and administering dangerous doses of a hazardous combination of medication not clinically indicated or justified, with patients and relatives powerless in their relationship with professional staff”.

Dr Jane Barton was found to have overprescribed diamorphine, and that while nurses, pharmacists, and other consultant doctors at the hospital were not responsible for ordering the prescriptions, they were aware of it but did not challenge it.

The 2018 report had not ascribed liability, and 72-year-old Dr Barton, now retired, had denied any wrongdoing, saying she “always acted with compassion”.