The inquest revealed that Mrs Poole, a retired school secretary, had become breathless just a week after giving up smoking.

She visited her GP seven times in the following few weeks, who eventually referred her to another doctor.

On April 19, she attended Northwich Infirmary to have some X-rays and an examination by Dr Toori.

He found a shadow on her right lung and decided to send her to Leighton the next day for an operation to drain the fluid and extract some tissue for diagnosis. An appointment was made for 10.30am the next day, but Mrs Poole was not taken to the treatment room until 3.45pm. The inquest was told that Dr Toori gave her a local anaesthetic and inserted a fine needle into the left lung. He then tried to draw fluid, but was having difficulty.

It was only when Mrs Poole pointed out that she thought he was operating on the wrong side, that he realised in horror he had made a mistake.

He checked she was feeling alright and then continued with the operation on the correct side.

Mrs Poole was visited soon after by her daughters Judith and Helen. She joked about feeling as though she had been through a round with Mike Tyson. Fifteen minutes later she said she felt hot and went to the toilet to take her tights off. But seconds later she staggered out, started to go blue and collapsed. A medical team was called but she could not be revived and died. Dr Toori admitted he had made an error. At the inquest he said: "By mistake I started the procedure on the left side. I have asked myself many times why I started on the left because I knew in my mind it was the right. I can't answer why because I don't know.

"In hindsight I also think I should have stopped and taken an X-ray."

Dr Ann Nicol, consultant pathologist at Leighton Hospital, ruled that the cause of death was likely to be a pneumothorax, the leakage of air between the lung wall and chest wall which compresses the lung.

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