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"Being at train station in Paris, when we were trying to get a room in a hotel or a train, and nobody could help us, was the low point," she admitted. "I did lose grip on my senses, especially having to pay one euro to use the toilet after queuing up for half an hour.

"Physically it was pretty exhausting. We've been on flights and in cars almost continuously since Sunday evening. For the last four nights we've had four or five hours sleep, so I need to get as much rest as possible."

Yamauchi, fortunately, is not the type of athlete to throw a star-shaped wobbly. Her own globe-trotting journey from club runner to the world-class elite, one of the more unusual stories in sport, has given her a very different perspective on such travails.

The 600 Euro taxi bill for the Lisbon-Madrid leg is dismissed with a philosophical shrug and recounting of the driver's reaction when she told him the destination ("'I'm so happy you're in my taxi! I'm going to make a week's wages in one night!'"), the subsequent hardships thrown into relief by another taxi-based conversation.

""The driver who took us to Le Touquet was a Cambodian man in his 60s. He told me about how he lost his wife and all his children in the war, which kind of put life's ups and downs in perspective."

Yamauchi has never been one to take the easy route. Eight years ago she was a career diplomat, working for the in Tokyo, happily settled down with her Japanese husband Shige. Running was for fun, and nothing more. The idea of succeeding Radcliffe as Britain's premier distance runner was as far-fetched as the idea of a volcano stopping play.

Yamauchi had been a talented runner as far back as her student days at Oxford University and the London School of Economics, where she was coached by the same man as - long-distance legend, supposed inspiration for the and now race director for London. But a year after coming home 38th at the European cross country championships in 1997, she abandoned athletics in favour of her burgeoning civil service career.

It wasn't until her 30th birthday in 2003 that she returned to serious training, and only in 2004 that she ran her first marathon. She got a stitch and had to stop to go to the toilet. Despite that, she clocked a very respectable 2hrs 39 mins, and an idea took root: take unpaid leave from work, train as a full-time athlete, and see how far she could go.

The results have been remarkable. As the graph below shows, she has improved her personal best steadily with every passing year, to the point where she finished second behind Germany's Irina Mikitenko in London last year and lines up this time around as a serious contender for victory.

Her secret? Hard work, attention to detail, and more hard work. No-one ever said marathon running was glamorous.

"It's not rocket science," she has said. "All elite runners simply have to train hard and ensure other aspects of their lives support their running.

"Beyond that, I've had a lot of support from my husband. I've paid more attention to recovery, which enabled me to train without injury for long periods of time, and I've built the confidence to risk setting off at a fast pace in big races."

Yamauchi had hoped to build on that second place with a strong showing at last summer's World Championships, only for two different foot injuries to rule her out - "completely crushing". Her preparations for London have also been affected by the long lay-off, but she has drawn strength from both a recent course record at the New York half-marathon and the deeds of another Briton in Berlin.

"I was inspired by Jessica Ennis, because she broke her foot in several places before Beijing and came back amazingly. I'm hoping to take a leaf out of her book."

The forecast for this Sunday in London is not ideal for marathon runners - 21 degrees, winds of up to 10mph, clouds building during the day to stoke up the humidity.

Yamauchi won't mind. For one thing there's Paula's shadow to step out from; it's five years since Radcliffe ran in London, but in the public's mind, she's still the one to beat.

More simply than that, she's just glad to be here. No matter what the sages might say, sometimes the journey is nowhere near as much fun as the arriving.