He has already run 16 marathons since Christmas, but a factory worker will be taking on his toughest challenge for a military charity this month.

Alan Lamb, 44, from Hall Road, Cromer, hopes to raise £1,000 for Help for Heroes by running from London to Brighton in one day on May 25.

He wants to complete the gruelling 62-mile route from Richmond Park to Brighton Racecourse through Surrey, Sussex and the South Downs in 13 hours.

Mr Lamb said: 'It is not daunting. I'm really excited about the event. I feel I can do it. My positive mental attitude is there and I'm up for the challenge. My friends and family think I'm crazy.'

To train for the event he has run the equivalent of 16 marathons, 26.2 miles, around north Norfolk on weekends and between 10 and 13 miles twice a week.

The furthest he has run on one occasion was 30 miles.

Mr Lamb raised £1,500 for Help for Heroes in 2011 after he completed the Barcelona Marathon in 3hrs 54mins.

He also raised £500 after he finished the Tough Mudder – an extreme 12- mile obstacle course designed by the Special Forces – in May last year.

Mr Lamb added he wanted to raise money for Help for Heroes because he wanted 'to do his bit' to support servicemen.

Participants who run from London to Brighton, of which there will be about 500, have to complete the challenge within 15 hours.

People can also walk the 62 miles and they have to finish the route within about 24 hours. Up to 1,000 people are expected to walk the route this year.

Last year the fastest time from a runner was 11hrs 26mins.

Mr Lamb first learned he enjoyed running while he was a pupil at North Walsham High School and between the ages of 16 and 23 he completed 40 half-marathons, including the Norwich Half-Marathon three times.

'I enjoy the freedom of running. You can clear your mind and you are in the fresh air. It is also a cheap way to keep fit,' he added.

He wants to continue fundraising for Help for Heroes and is planning to cycle from Lowestoft to St David's in Wales over three days with a friend.

To donate, visit www.bmycharity.com/alanlamb, email lambvista@aol.com or call 07795 517055.