A car is being loaded on to a breakdown trailer. Its owner gives Richard Dunwoody a wry look. "Hello!" returns Dunwoody brightly. "Got it sorted? Well done."
And on he marches. If cars let you down, from time to time, it is only because the internal combustion engine has no fear of failure.
This is the most Sisyphean of all the brutal tests the former champion jockey has set himself over the years. When the scheme was first proposed to him, it seemed a pretty leisurely aspiration: 1,000 miles in 1,000 hours. Dunwoody is fitter, at 45, than most men half his age, and could easily walk 24 miles a day and leave ample time to eat, recuperate and sleep. But there was a catch. He was not being asked to walk 1,000 miles in 1,000 hours, but the same mile, every hour, for 1,000 hours.
Even by walking a mile back-to-back, either side of the chimes, he has condemned himself to barely an hour's sleep at any time, day or night, rain or shine, for six weeks.
As he strides past the crippled car, Dunwoody is comparing the enterprise with his expedition to the South Pole last year. Surely this epic monotony, this endless Newmarket street, is more corrosive than an environment so full of brilliance and danger? He laughs. "Antarctica? The most unstimulating place in the world. Apart from some of the high cloud formations, which were amazing. When it wasn't a white-out, that is. Otherwise you've got snow, and you've got ice. The last seven degrees were a nightmare. You just had to grind it out. You had nothing. Do the life thing, you think. Sort your life out. Well, you did that on the first day. Yes, you said, I'll do that when I get home. That's sorted."
Some look at all these restless adventures, and imagine they see unfinished business in that respect. A mile or two on the road with Dunwoody, however, soon corrects that misapprehension.
This latest assignment marks the 200th anniversary of an identical endeavour by one Captain Barclay, who achieved many exotic feats of pedestrianism. On his 607th mile, Barclay fell asleep on his feet, and an assistant had to beat him with a stick to get him going again. He had a 1,000-guinea wager to concentrate his mind; Dunwoody, the money he is raising for charity.
He is past 300 miles already, and remains in remarkably robust spirits despite averaging just four naps each night. But 10 July remains a long way off. All through Royal Ascot, this week, and then Wimbledon fortnight, up and down from his hotel to the war memorial and back.
He has a team of helpers, umpires and friends to sustain him, and none has so far needed a stick. A P McCoy, the champion jockey whose competitive addiction owes so much to Dunwoody's pioneering example, predictably set the fastest mile to date, despite pushing a wheelchair. Last Thursday, Dunwoody's mother was putting in a mile of her own ("she took up golf when she was 70") and Paul Bamford, a Racing Welfare beneficiary confined to a wheelchair after a riding accident, pushing his way through 24. Also on hand was Mike Tomlinson, widower of the fund-raising athlete, Jane.
Dunwoody talks with humility of their example. "That's been one of the best things about what I've been doing, the inspirational people you meet," he says. "What sets A P apart [from other jockeys] is that he's so mentally tough. But you come across these people, from many other walks of life, and then you really do see what mental toughness can be."
For Dunwoody as a rider, as for McCoy after him, reckless physical courage had paradoxical roots in another type of dread. It nourished him then, and again when he shed 40lb pulling his own sledge across the Antarctic. "There's always that fear of failure," he admits. "Some sportsmen, like Roger Black, say they've never had it. Psychologists say you shouldn't be afraid of failure. If it affects you that badly, then maybe you shouldn't do it. But it always affected me as a really positive thing, really drove me. And it does now, doing this. If I get ill, fine, I've just got to cope with it. But even walking up and down here, you can get injured, do something stupid."
Dunwoody is goaded by those who imagine that he somehow yearns, tragically, for the faded intensity of his riding days. For here is a man who shows restlessness in a very wholesome light. Dunwoody only has one life, like everyone else, but has an unmistakable sense of privilege in living it so thoroughly.
"What are they going to say in 25 years' time, if I'm setting myself new challenges?" he asks. "They'll say I'm still restless. All I am is very, very lucky, to be able to do these things. I've always liked a challenge. Every time you get on a horse, you're being challenged to get the best out of it. If you run a marathon, you're not competing against however many thousands are also taking part, you're competing against yourself. Look at Ranulph Fiennes, climbing Everest at 65."
Reaching the war memorial once again, he remembers the men whose failure he redressed in the Antarctic. He recalls the newspaper advertisement placed by Shackleton: "Men wanted for hazardous journey. Small wages. Bitter cold. Long months of complete darkness. Constant danger. Safe return doubtful. Honour and recognition in case of success."
He smiles. "That was 1913. Five thousand people replied to that advert. And the 28 who went on it, and somehow, amazingly, survived two winters in Antarctica, then came back to World War I. And half of them got killed. If we'd been born in a different time..."
But his sense of pity, for the men doomed to have their names carved on the memorial, is tempered by admiration for the spirit that produced the responses to such an unpromising invitation. His reflections are that of a man who is not lost, but on a journey. "You've got to make the most of everything," he says. "I've had some incredible experiences, and I wouldn't give any of them up. I could go home and try and get a job in an office. No, thank you! I feel very blessed."
Poles apart Dunwoody's spirit of adventure
*Three times champion jump jockey
*1,699 career wins – including seven on Desert Orchid
*Retired in 1999, aged 35, when told that another neck injury would cost him his right arm. Other achievements
*Finished second in team race to magnetic North Pole.
*Adventure rides in Ecuador, Kyrgyzstan, Afghanistan.
*Learnt cross-country skiing by crossing Baffin Island, hauling 50kg sledges.
*With Doug Stoup, the first to reach the South Pole by a route originally attempted by Shackleton.
*The "Mongol Derby" in August, a 1,000km race across the Mongolian steppes on a relay of 40 ponies. "And I want to go to the North Pole, before we have to swim there..."
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