Greenest ironman who leaves no trace

He will swim twice the length of Oxford Street, cycle the distance of the M25 and run a full marathon in one go - all without leaving a footprint. A carbon footprint, that is.

Londoner Jon Alexander will ditch his regular trainers, swap his carbon-fibre bike for a bamboo one and wear recycled-fibre clothing to become the first eco-competitor in an Ironman-length triathlon in Barcelona.

Only attempted by a few thousand people a year, races in the gruelling series take about 12 hours to finish and are regarded as some of the most challenging endurance events. They include a 2.4-mile swim, a 112-mile bike ride and a 26.2-mile run.

Mr Alexander, 27, an environmental strategist at a Soho advertising agency, has run four marathons and rowed for Great Britain at under-23 level. He is training by swimming in the Serpentine, trudging parks and towpaths and covering miles of the city's roads by bike.

But his training and preparation are focused not just on the physical challenge but on the environmental one.

He will travel to Challenge Barcelona, which is on 4 October, by Eurostar and overnight train, and will auction off his bike and other reusable pieces of his environmentally-friendly kit after the race to raise money for charity.

He will eat a vegetarian diet, getting protein from beans, pulses and cheeses and dreaming up recipes "using eggs in ways that the average person never thought possible". He will also munch on fair-trade, organic sports nutrition products.

Mr Alexander, who lives in Wandsworth, wants to draw attention to open spaces available for sport, and aims to raise funds and awareness for the Wilderness Foundation, a charity which encourages city-dwellers to become connected to nature and wild places.

He said: "If I can inspire people to find more of a place for nature in their lives, and raise money for those who otherwise wouldn't get the chance, I will definitely feel like I've succeeded."

The Ironman events culminate in the Ironman World Championships in Hawaii every October, although this is a problem for Mr Alexander: "I don't think you can get the train to Hawaii."