A pensioner who was told he might have lung cancer had a cashew nut stuck in his lung for 18 months, a hospital said yesterday. Derek Kirchen, 67, feared the worst when baffled doctors told him they could find no explanation for his eight bouts of pneumonia or why he was frequently collapsing.

The retired construction worker had numerous tests and x-rays at the Queen Elizabeth hospital in King's Lynn, Norfolk, but they failed to reveal the reason for his mystery illness. He was warned he might have lung cancer.

But to his relief, a doctor cracked the problem during a minor operation. A consultant respiratory physician, Syed Tariq, threaded a camera tube down Mr Kirchen's throat to discover a cashew nut lodged in the patient's left lung.

Dr Tariq pulled it out, using claws attached to the camera, and saw that the nut was completely whole, with some of its skin still attached.

Mr Kirchen was under a general anaesthetic during the procedure, but when he came round he was shocked by the doctor's discovery.

"I just don't know how it got there, it's a complete mystery. When I came round in the treatment room all the nurses were giggling and laughing as they couldn't believe it was a nut," he said.

"I am feeling fine now, and am just thanking my lucky stars it wasn't cancer. I can't remember choking on a nut. It's ironic really as I don't even like the darned things."

Mr Kirchen added that he had last eaten a cashew at Christmas 2004, meaning the nut had been stuck in his lung for a year and a half.

Dr Tariq, who spotted the suspicious little black lump on camera, said the medical team were very relieved: "I was pleasantly surprised when I found it as we were expecting lung cancer."

Mr Kirchen's experience is not unusual, according to the hospital. A spokesman said yesterday: "People choke on nuts and without realising part of it gets stuck in their lung. It causes similar symptoms to pneumonia.

"The problem was that because a nut is organic, it doesn't show up as being a foreign body on an x-ray. When the x-ray came back it also had similar markings on it that you might expect to see with somebody who has cancer."

Mr Kirchen is expected to make a full recovery. He was discharged from the hospital at the end of last week and is recuperating in a nursing home.