Dr Thompson contacted the coroner to say what he had done

A verdict of death by natural causes was recorded on Sarah Lloyd, 91, of Trefeglwys near Newtown, Powys.

The inquest heard she had been given the much stronger diamorphine instead of morphine at Llanidloes hospital.

Coroner Geraint Williams said it was impossible to be certain what killed the heart patient in March 2005.

Mrs Lloyd had been admitted to hospital a few days earlier and had recently suffered major heart problems.

Giving evidence, Nurse Justine Phillips said she knew the difference between morphine and diamorphine but she could not account for her actions.

She said she thought Dr Thompson, a Newtown GP who is part of an out-of-hours service, had meant diamorphine and not morphine.

But Mr Williams said it was not clear that Ms Phillips knew the difference between the two drugs.

Mrs Lloyd had been treated with "compassion" prior to her death Coroner Geraint Williams

The coroner said he had been assured by Powys Local Health Board that steps had been taken to educate Nurse Phillips and that the LHB were satisfied that these were professional people who had made a "catastrophic" yet "genuine mistake".

Giving evidence, Dr Thompson said he was called to the hospital shortly after midnight on 25 March 2005.

Hours earlier another GP with the ShropDoc out-of-hours service had treated Mrs Lloyd, but her condition at night had not improved.

After examining the pensioner, Dr Thompson diagnosed she may have had a urinary tract infection.

He told Nurse Phillips to treat her with intraveneous antibiotics and fluid.

But Dr Thompson said Mrs Lloyd was also agitated and asked that Nurse Phillips adminster 10 milligrammes of morphine if this persisted.

"I did not want her to die in a painful and distressed state and discussed this with her two sons," said Dr Thompson.

Clearly written

"They were happy with the treatment I was prescribing, of 10mg of morphine when needed."

Dr Thompson explained that morphine was generally given to relieve pain but it had the side-effects of slowing down breathing and sedating patients.

He returned later that morning to certify her death. It was then that he discovered the error, in her patient notes.

"It was a genuine error - and in my opinion it made no difference to the outcome of the lady's life."

Dr Thompson admitted to altering Mrs Lloyd's notes whilst Nurse Phillips was present.

Nurse Phillips told the inquest that she believed she had been asked to administer diamorphine, although morphine had been clearly written in the patient's earlier notes.

She said Llanidloes hospital had "never stocked morphine" as far as she was aware and she had never used it.

The three staff suspended had resumed their duties

But she said she knew the difference between the drugs.

"We went into a room and Dr Thompson explained to me that he had prescribed morphine and I had given diamorphine," she told the inquest.

"He explained it was nearly twice as strong. I went into terrible shock and could not believe what had happened."

Another nurse had, under hospital procedures, witnessed the drug being administered - and she also had not noticed the difference, the inquest heard.

Dr Thompson called the coroner personally to report what had happened.

The three members of staff had been suspended, pending investigation, and had now resumed their duties.

The cause of death was given as cardio-respitory failure in "an extremely old woman" after she received diamorphine.

Mr Williams said he believed Mrs Lloyd had been treated with "compassion" prior to her death.

But he said that by changing the notes they had "fallen below" professional standards.

But Mrs Lloyd's son, Harcourt Lloyd, praised the work of the health professionals in a written statement.

The inquest also heard from pathologist Dr Derek James who said Mrs Lloyd was a woman "who might have died at any time".