Both the police and the Crown Prosecution Service insist it was right to charge a senior nurse at Airedale General Hospital with the murder of three patients, despite an independent report concluding their deaths were unlikely to have been caused deliberately.

An inquiry has severely criticised bosses at the Steeton hospital for allowing systemic failures between 2000 and 2002 in which senior night duty nurses were able to inject opiates without prescription.

But the report says that murder suspect Anne Grigg-Booth was unlikely to have set out to “deliberately harm” hospital patients.

The hospital trust has also been criticised for failing to be alert to the problem six years earlier when a patient died two hours after an intravenous injection of an opiate by a Night Nurse Practitioner (NNP).

The findings of the independent report by Yorkshire and Humber Strategic Health Authority into the deaths, between 2000 and 2002, and the subsequent arrest of Grigg-Booth were published on Tuesday in a 5,000-word report.

The 52-year-old, who had worked at Airedale for 25 years, died of an overdose at her home in Nelson in 2005 as she awaited Crown Court trial on the murder charges as well as one charge of attempted murder and 13 counts of causing grievous bodily harm by administering drugs overdoses to 12 other patients.

The police case against her was discontinued, but this week the police and the Crown Prosecution Service (CPS) said: “It is, of course, a matter for the inquiry to come to its own conclusions, but we are satisfied that the West Yorkshire Police investigation was thorough and the decision by the CPS to prosecute was the correct one.”

However, Grigg-Booth’s solicitor maintains she should never have been charged with murder.

Paul Fitzpatrick said investigating detectives had not believed her when she told them about practices at the hospital.

Though the inquiry was critical of her, it concluded they thought it unlikely she deliberately set out to harm patients and that “notwithstanding certain flaws in her character” almost without exception, medical and nursing colleagues recognised that she was a hard-working, experienced and caring nurse who could be relied on in a crisis, he said.

The SHA inquiry was not started until last year and its findings were made public at the Yorkshire and the Humber Strategic Health Authority headquarters in Leeds.

Facing the press was a panel made up of Bridget Fletcher, nursing manager at Airedale General Hospital, Jo Coombs, director of nursing at NHS Bradford and Airedale, Andrew Cato, medical director at Airedale, Eddie Kinsella, an inquiry team member and Professor Sue Proctor, chief of nursing at the SHA. None of the managers involved in the Grigg-Booth scandal are now working at Airedale NHS Trust.

Grigg-Booth, who at one time lived in Cowling, was dismissed by the trust along with a manager, two other NNPs were downgraded, another took early retirement and a second manager resigned.

The report emphasises that Grigg-Booth was not a rogue nurse in the mould of Beverly Allitt who murdered four children at a Lincolnshire hospital in the early 1990s.

Grigg-Booth and other NNPs who were administering drugs without a prescription were victims of a management systemic failure, it states.

Mr Kinsella said: “She should not be demonised because she and others believed they were acting with the authority of the board.

“There was a schism between what the board perceived to be happening at night and what was actually happening and that led to this tragedy.”

He was referring to remarks in the report which state that “the most striking feature was in the disconnection between what was happening on the wards at night and what the board knew. The board had no idea”.

Mr Kinsella said Grigg-Booth did everything in the open and made scrupulous records of drugs she administered. Once, she wrote to a senior manager admitting what she was doing was illegal.

The system was introduced as part of the Government’s New Deal policy to reduce the hours of junior doctors, leaving the hospital at night to be run by the NNPs who could phone doctors for advice. It was recorded in 1996 that a patient died two hours after an NNP administered an opiate.

Six years later, the report reveals, the death of a patient two hours after an injection of an opiate set off an investigation by the hospital trust and the eventual police probe.

The report concludes: “If this conduct were truly against hospital policy, it should have been picked up and stopped six years earlier, well before any of the incidents we have reviewed.”

It says the position now is “very different”.

Mrs Fletcher said: “There are now no NNPs at Airedale and a 24-hour system has been introduced with highly-qualified nurses working on a 24-hour shift basis. There is no disconnection between what goes on during the day and at night.”

The hospital had been awarded Foundation Trust status which had helped to focus on improving systems, and safety was now as good as it could be, she said.

“We hope this final stage of the process has now fully explained the details concerning each patient as well as the action of Sister Grigg-Booth, other staff and the trust at the time eight years ago,” said Mrs Fletcher.

“The trust has made significant improvements, particularly since 2005, thanks to the enormous efforts of the trust board and staff.”

The report makes 11 recommendations, including that the Trust should make time for periodic reviews to ensure systems and processes do not take precedence over patients.