Some days his condition is so severe that he can't eat, sleep or even get out of his own front door.

But tomorrow Glen Gilmore, despite his obsessive compulsive disorder, will take part in the Bristol 10k run.

Mr Gilmore, 45, will pound the streets with 15,000 other runners as they race around the city centre and the Portway.

While other competitors will be worrying about their times and finish positions, Mr Gilmore will be focused on how to deal with his fear of cracks in the pavement and threatening shapes and shadows.

As part of his coping mechanism, he will be carrying pieces of cloth and tissue in his hands, eating raisins and popping little bits of paper into his mouth as he goes around.

Mr Gilmore, of Bantock Close, Knowle West, lives on his own and struggles to the most basic of everyday tasks, including making a cup of tea.

He said: "Most people have problems with cleaning or washing their hands, but I see and touch things in certain ways. When I touch door handles I see in my mind that I am leaving my friends and family behind, and then see them die. I have to go back to the door and retrieve them. I can be stuck for hours at a time, even days.

"It is the same with cracks in the pavement, and shapes and shadows. Where I put my foot down on a crack it leaves my friends and family there, so I have to go backwards and forwards to retrieve them."

By carrying things with him it helps him focus away from his worries, and effectively bring his friends and family with him.

He said: "I have a pouch I can dip into, and I can throw the paper away at the end of the race.

"I am pretty nervous about the race, but I know I can do it. I never thought I could do something like this. If you spend your life trapped in your own head, your world can get very small and dark."

Mr Gilmore has suffered from severe OCD since the age of seven, but has no idea what first triggered it.

The condition has dominated most of his life, leading to countless hospital admissions and treatment programmes.

He also has a specialist medical team looking after him at home.

Other sufferers repeatedly check that the gas is off or wash their hands, but Mr Gilmore's anxieties rule his life.

His rituals stop him eating, sleeping, meeting people and even making a cup of tea. Until recently he could barely leave his home, and had to have special training to build up his muscles because of lack of exercise.

His OCD is so severe he could even have to have an operation on his brain.

But two years ago, a carer took him to Windmill Hill City Farm in Bedminster, where he became involved in the UK online centre.

He began learning about computers and the internet, and took up painting, drawing and jewellery-making classes, and volunteering to help other people with mental health issues through computer training.

He also met Peter Holthuis, who became his mentor, tutor and eventually his running partner.

Mr Holthuis, 48, a community ICT officer and former psychiatric nurse, said: "I am a runner myself, and in the winter I put it the idea of the 10k run to him.

"He took one look at me and thought 'Why on earth are you asking me this? I can barely cross the road sometimes.'

"I basically challenged him. He went away and thought about it, and came back and said he was up for it."

The pair have been training once a week at Victoria Park in Totterdown.

It has been tough going – Mr Gilmore occasionally jumps into the road from pavements to avoid cracks – but his coping techniques have improved.

Mr Holthuis, of Richmond Street, Totterdown, said: "He has got better and faster. Now we are not just looking at getting around the course, but doing it in a good time."