Ellen MacArthur says that she'll never race again

Four years after becoming the fastest person to sail around the world alone, Dame Ellen MacArthur is giving up ocean racing – to save the planet. The sailor, the castaway on today's Desert Island Discs on Radio 4, says she is so anxious about the threat to the environment she will abandon any new marine expeditions.

Her conversion came during a journey to South Georgia in the south Atlantic where she spent two months investigating the plight of the albatross, the giant sea-faring bird which is under threat from hooks used in long-line fishing.

Dame Ellen, 33, who was honoured in 2005 after her record-breaking circumnavigation, said: "After being on South Georgia, the more I researched, the more frightened I got. And that has scared me to the point where I can't go back to sea and go round the world again because this really matters."

Her record of 71 days and 14 hours was broken last year by Francis Joyon, a French sailor, who knocked 14 days off the time.

Dame Ellen – who says she was inspired to a life of adventure by reading Arthur Ransome's Swallows and Amazons books and reveals her favourite record to be Don Henley's "The Boys of Summer" – had previously broken his earlier record by one day and eight hours.

Referring to their great rivalry and the temptation to reclaim the record, she tells the programme's host, Kirsty Young: "There is a part of me that wants that record back, but something's stopping me from doing it."

South Georgia changed her attitude towards her life and her view of the world. "Down there, for the first time, I actually stopped," she says. "I realised that on land we don't see things as precious any more. We take what we want. And it started to make me think. I was looking at plans for the future and it hit home.

"This world, that I thought as a child was the biggest, most adventurous place you could imagine, is not that big. And there are an awful lot of us on it. And we're not managing the resources that we have as you would on a boat because we don't have the impression that these resources are limited."

She adds: "I didn't think anything in my life could eclipse sailing. But how brutally selfish it is to go off sailing around the world, even when you are achieving your dream?"

Her new priority in life is sustainable living, but she will not abandon her charity work, which helps children with cancer and leukaemia.

"When you sail on a boat you take with you the minimum of resources. You don't waste anything. You don't leave the light on; you don't leave a computer screen on. And I realised that on land we take what we want."

She will test her new-found principles by building a house on the Isle of Wight which has been designed on ecological grounds.

It has solar panels to heat the water, under-floor heating, and a Rayburn stove plus two wood-burners. The house's walls are 2ft thick with 8in of insulation.

She still sails, but just for pleasure and for her charity. "So, will I invest four years again into sailing round the world? No. This new understanding has, for me, become far more important," she says.