"My family think I'm crazy. I think they are a little bit worried for me - which is OK, because I'm worried for me too."

For football agent Matt Kleinman, a serious challenge is looming next month.

The Marathon De Sables (MDS) is a 251 kilometre race carried out over six days in the 50-degree heat of the Sahara Desert.

Every year, more than 1,000 runners complete one marathon each day while carrying all their food, clothing and sleeping gear.

Mr Kleinman, a 38-year-old Maccabi League footballer who had never completed a marathon when he signed up to the challenge, said: "It sounds like fun, doesn't it? If you're a psychopath."

He admitted that though he kept himself fit, the task was "a totally different proposition. It's really flagged up all my weaknesses, and I think my age is starting to come through.They say it's the toughest foot race on Earth, so I want to be able to tick it off before I die - hopefully I won't die while I'm out there."

Mr Kleinman has used unorthodox training methods, including travelling to South Africa in November for his first marathon. He has also been running around in full kit, with a protective covering stitched on to his shoes to prevent sand getting in and causing the huge blisters for which MDS is infamous.

Runners require 2,000 calories a day, but, Mr Kleinman said, "being a nice Jewish boy I like my food, so I'm going to take more".

He has so far raised more than £6,000 in sponsorship for Great Ormond Street Hospital and breast cancer charity Future Dreams, set up by his Maccabi league team-mate Craig Henry, whose mother and sister died from the disease.