Britain's Overall not overwhelmed by the Kenyan marathon challenge

This time last year Scott Overall was selling running shoes in the Clapham branch of Sweatshop. This morning he will line up as the leading British hope in the final athletics event of London 2012, the men's marathon.

It will only be the 29-year-old's second race at the 26.2 mile distance. His first, in Berlin last September, elevated him to the status of Olympian and full-time athlete. "It changed my life," Overall said, without exaggeration.

The Blackheath and Bromley Harrier finished fifth in a world-class field in 2hr 10min 55sec. It was the fastest time by a British marathon man for six years and 65 seconds inside the Olympic A qualifying standard. It earned him a contract with sportswear company Adidas and with the Virgin London Marathon.

A former pupil of Orleans Park School in Twickenham, Overall spent much of his youth training with Mo Farah at Hounslow Athletics Club. He landed a scholarship at Butler University in the United States and still splits his time between training with the Team Indiana elite squad in Bloomington and with his long-time British training partners in south-west London.

His mission today is to challenge for a medal. That will be a big ask against a world-class field featuring a trio of Kenyans intent on honouring the memory of Sammy Wanjiru, who won gold in Beijing but tragically died after a fall from the first-floor balcony of his house in May last year. Overall has raced sparingly in the build-up – just twice since the spring.

In May he finished third in the Bupa London 10,000 and, three weeks ago, he won the Bupa Great North 10km in Gateshead.

"The trick with the marathon is to make sure you go into the race fresh," he said. "It is always better to go into a marathon under-trained than over-trained."