A hospital has apologised after a Woodford Green woman suffered a catastrophic brain injury when she was accidentally given a “toxic” overdose of an unlicensed and unapproved drug while in intensive care.

Yvonne Hewitt, 54, underwent surgery to fix her ureter, which was damaged in a previous operation, but was given a dose of lidocaine so high that she had two heart attacks.

She died two years later in April this year from organ failure, but her family say she effectively died that day.

Yvonne's nurses failed to notice she was having a heart attack for several minutes as the alarm in her heart monitor was muted. This led to her suffering an unrecoverable brain injury.

A serious incident report into the blunders at University College London Hospital (UCLH) revealed that nurses gave Yvonne a dose of lidocaine for pain control - a drug that had not been approved for use by the hospital's use of medicines committee - that was meant for a patient who had an irregular heartbeat.

Nurses administered the wrong amount as there was no information on the two types of dosage on the ICU computer system - despite a "near miss" three months before when another patient was almost given an incorrect dosage.

Yvonne's family are taking legal action against and are being advised by solicitors from London law firm Osbornes Law.

Yvonne's sister Dianne said: "I feel like there was an institutional failure by the NHS in my sister's case as she was failed from start to finish.

"There were just so many horrors that she had to deal with and they ultimately killed her, and although she died two years later, I feel that the people who were meant to care for her in UCLH struck the final blow."

Yvonne first went into Homerton Hospital in April 2015 to remove her right ovary, but suffered internal bleeding when her ureter was severed. She went into septic shock and was rushed into intensive care.

The following month she had a nephrostomy - a tube and a bag - inserted.

On December 9, 2016, Yvonne was admitted to UCLH to repair her ureter and was then transferred to intensive care at Westmoreland Street, also part of UCLH.

Dianne said: "She was apprehensive about the operation, but she was excited about getting her life back.

"I thought we were almost there, and we were. The operation was a success.

"She was in a lot of pain and said that she felt like she had been kicked in the chest by a horse. She was in good spirits and laughing despite the pain she was in as that's the kind of person she was.

"When I left her she was fine and there was nothing untoward.

"I said I would see her in a few hours, and I never spoke to her again."

Yvonne's husband Owen added: "The operation seemed to have gone well but she said she was in a lot of pain. When I left her I told her to try to stay strong until the morning. The last thing that she said to me was that she was going to be okay."

Dianne and Owen were later told that Yvonne had suffered a catastrophic brain injury.

Owen said: "I lost my best friend when Yvonne suffered that brain injury and my life has never been the same.

"How could they have given her a drug that wasn't even approved and which led to her having two heart attacks?

"It is negligence of the worst kind and I am devastated by what happened."

UCLH has admitted liability in the case.

A spokeswoman for the hospital said: "We would like to offer our deepest sympathies to Mrs Hewitt's family and loved ones.

"We apologise unreservedly that she did not receive the standard of care that our patients expect and deserve.

"We investigated this thoroughly and have taken a number of steps to ensure that a similar case does not happen again."