Sara Black's London finish in 3:27 came six days after she completed the Boston Marathon suffering from hypothermia.

"I actually don't feel too bad," said the 42-year-old mother-of-three. "I felt terrible after Boston. At mile 20 in London, I did find myself saying: 'I can't complete this.' But after pulling off to the side I hobbled to the finish line. I thought: 'I've got to do it.'"

The Highgate runner's performances have earned automatic qualification for both marathons next year. And she has an even more ambitious target in her sights.

"I've put my name down for the seven-day marathon in the Sahara. I like a challenge."

Her love of physical trials started with a 5km charity run. It was like "opening up a packet of Pringles. The more you have, the more you want."