The golden hurdle to overcome is £1,252,466, the record for the most amount raised in a single event. It is held by a runner in last year’s marathon.

Redgrave, 44, retired from rowing after winning his fifth gold medal at the Sydney Olympics in 2000, but he has lost none of his competitive spirit.

The following year he set himself a target to raise £5m for children’s charities over five years. The deadline runs out in November and he is still £1.7m short. Redgrave says in an interview in today’s Sunday Times Sport section: “Raising money has become a way of life over the past five years, but this is the big one.

“I’m never going to win the marathon — look at me. Do I look like a marathon runner to you? No — this is my best shot at a victory of any kind in the marathon. Even if I have to crawl to the line, I’ll do it. Last time I ran the marathon, I had to walk downstairs backwards for a week because my legs hurt so much, so please sponsor me.”

The money raised will go to three causes: the Association of Children’s Hospices, Children with Leukaemia and the Steve Redgrave Trust’s schools fitness and education project.

Last year he raised £800,000 towards the £5m target by running the marathon in 4 hours 21 minutes, but he decided to postpone a record attempt until this year so others could maximise their efforts to help victims of the tsunami disaster.

In doing so, he let through Steve Chalke, a Baptist minister and founder of the homeless charity Oasis Trust, to set the world record for fundraising. Chalke eclipsed the previous figure of £1.19m raised by Sean “Diddy” Combs, the hip-hop singer, in the New York marathon in 2003.

Redgrave has plenty of competition in his bid to beat the record. Later this month Ian Botham, 50, the Ashes-winning cricketer, is set to announce a new charity walk in which he hopes to outdo the £1.1m he raised for Leukaemia Research marching from John o’Groats to Land’s End in 1985.

Next month Alan Shearer, 35, the Newcastle United striker, will donate the proceeds from his testimonial match between Newcastle and Celtic to various funds, including the NSPCC. The 52,000 tickets, costing up to £25 each, sold out in 48 hours.

There could yet be a late entry for the race to make the most money. Roy Keane, the former Manchester United captain, has still to announce what will happen to the proceeds of a testimonial at Old Trafford in May between United and his current club Celtic.

Keane, 34, once accused Niall Quinn, his former Republic of Ireland team-mate, of behaving like Mother Teresa in donating the £1m proceeds of his testimonial match at Sunderland in 2002 to charity. But now even Keane is expected to donate much of the proceeds of his benefit match to charity.

This week Anna Kournikova takes part in a charity tennis doubles match in Florida with Jim Courier, John McEnroe and Chris Evert to raise money for Courier’s foundation for “at risk” children. The tournament raises £250,000 annually.

The surge to raise big sums for charity by British sports stars is partly explained by the amounts they can now earn in their careers for their retirement by sponsorship deals and partly by their continued fitness in later life.

Redgrave said last week: “I am feeling refreshed, positive and ready to attack my training. The only blot on the landscape is a sore tendon behind my knee.

“The London marathon is now three weeks away and I am cautiously optimistic that I will be ready, willing and able. Bring it on!”

Shearer is equally enthusiastic about his testimonial, where ticket sales will be swelled by sponsorship. It is hoped well over £1m will be raised from his farewell game. “I hope that by pledging the money from my testimonial to charity and worthy causes, people less fortunate than myself will also benefit in some way from my football career,” he said.

The charity bug is spreading. Geoff Thomas, the former Crystal Palace captain who raised £170,000 by completing the 2,200-mile Tour de France last year after recovering from chronic myeloid leukaemia, is holding a rematch of his team’s 1990 Cup Final against Manchester United this week to raise more for leukaemia charities.

Lindsay Boswell, chief executive of the Institute of Fundraising, said: “It is fantastic to see so many sports stars using their high-profile position to benefit good causes.”

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