A grandmother died after being accidentally prescribed 10 times the required dose of morphine, an inquest heard.

Jean Martin, 81, of Cleator Moor, was admitted to Cockermouth Community Hospital on February 21 after treatment at Carlisle's Cumberland Infirmary.

But when she returned to her Stafford Court home the next day, her complex combination of pills included 200mg of morphine twice a day instead of the required 20mg. She took two doses of the drug before the alarm was raised.

The inquest heard that, on February 23, the retired shop assistant appeared "zonked out". She was taken to the West Cumberland Hospital in Whitehaven, where the mistake was found.

Mrs Martin was given a morphine antidote, which improved her condition, and treated with antibiotics because of concerns she could develop pneumonia. But, after initially responding to treatment, she got pneumonia and died in hospital on March 5.

GP Dr Simon Desert, who treated Mrs Martin in Cockermouth, told the inquest her paperwork had not arrived with her from Carlisle, meaning Cockermouth staff could not draw up their paperwork as usual. Her notes and drug chart arrived later that day.

Dr Desert had to reissue Mrs Martin's drugs, which included a large number of medicines, as they had to be collated in blister packs to meet her care agency's needs. The court heard it was a very busy day with a number of complex cases being dealt with at once.

Dr Desert used a computer search tool to select the drugs. But when it came to sustained-release morphine, he said, he wrongly thought Zomorph was available in 20mg tablets. He typed "Zomo" and "20". Not realising the result was for 200mg tablets, he added them to the prescription.

A warning appeared about the dosage but Dr Desert had expected the warning for a 20mg dose. He did not spot the extra zero before signing the prescription and the pharmacy did not query it.

Dr Desert said: "I'd like to offer the family my condolences and my apology. It was apparent from February 23 that we made an error and for that I sincerely apologise. It will live with me until my dying day."

He added that he no longer worked in the hospital ward as Cumbria Partnership NHS Foundation Trust, which runs it, does not allow doctors access to the systems needed to carry out clinical audits of their own work. He said he believed it was necessary to be able to do that to identify systemic problems and improve safety.

The Castlegate & Derwent Surgery GP added that, after this incident, improved warnings had been added to the surgery's computers to flag up high dosages being added to prescriptions. He suggested the same could be done on the partnership trust's computer system.

The inquest heard that the partnership trust had brought in measures to try to prevent future errors. They included sending all prescriptions to its contracted pharmacy, Lloyds, and requiring pharmacists to check prescriptions against drug charts.

Discharge procedures had been tightened, with nurses checking that medication was correct. The trust had contacted its software supplier to see if its search function could be improved.

Coroner Kirsty Gomersal accepted the findings of a Home Office pathologist, who said Mrs Martin died of bronchopneumonia following opioid overdose consistent with a prescription error.

Recording a narrative conclusion, Mrs Gomersal added: "It's clear to me that Jean was a much-loved mother and grandmother. She was a lady who adored her family, who in return adored her."

The inquest heard that Mrs Martin had been married to the late John, known as Jackie, for 60 years, and had a son, a daughter and three grandchildren. Daughter Jacqueline Ellery said: "She was all for her family really. She absolutely doted on her grandchildren. Her and my dad, we used to joke that it was a marriage we'd aspire to."

The inquest heard that Mrs Martin was also famed for her Sunday lunches.

After the inquest, Michelle Armstrong, who represented the family, said: "Mrs Martin's family are devastated by the loss of a much-loved mam and nana. They are however grateful for the inquest process in exploring what led to the error which caused her to suffer an overdose.

"The family very much hope that lessons will be learned from her tragic death and safety nets implemented to stop this happening again. They would ask for their privacy at this difficult time to be respected."