A veteran runner has vowed to complete his 25th marathon despite suffering from a debilitating lung condition.

John Gwillim from Brightlingsea was diagnosed with sarcoidosis four years ago.

This rare disease causes growths in the lungs, leaving the sufferer feeling breathless, tired and generally unwell.

For the 46-year-old, the illness came completely out of the blue.

“I went to the doctor with a headache,” said the father-of-two, who lives in Tabor Close.

“I'd been feeling tired and had achy joints, but I thought it was because I was training for a triathlon.

“The doctor initially thought I might have leukaemia, as a lot of the symptoms are the same, like high levels of calcium in the blood.

“It was terrifying.”

He added: “It was hard when I found out it was sarcoidosis, because I’d never even heard of it.”

Since the diagnosis, Mr Gwillim has been on steroids to prevent the growths in his lungs spreading to other organs – medication he is likely to need for the rest of his life.

Despite this, his lung function has decreased by 30 per cent over the last six to eight months.

It has been a bitter pill to swallow for the keen runner, whose best marathon time was under three and a half hours.

“I was very fit and healthy before,” said Mr Gwillim, who works in a civilian role at Clacton Police Station.

“I loved running, especially the endurance side of things.

“It's been quite hard, as I do suffer with the side effects of the steroids, like the increased appetite and weight gain.

“But I have to stay positive.

“I am inspired by people like Lance Armstrong, who won the Tour de France after having cancer.”

Determined not to let his condition rule his life, Mr Gwillim signed up for this year's London Marathon in aid of the British Lung Foundation.

“It will be a walk,” he admitted.

“It's going to be difficult for me to take things slowly, and I'm struggling to think about what it will be like.

“But I will have to listen to my body.

“I just want to get round and complete my ambition of getting to 25 marathons.”

Mr Gwillim will certainly stand out in the crowd as he walks around the 26-mile course – as he'll be dressed as Fred Flintstone.

“It was something I came up with after talking to my wife Sally and daughters Tasha and Jemma,” he explained.

Mr Gwillim has already raised £720 for the British Lung Foundation.

If you would like to contribute, visit justgiving.com/johngwillim