What started out as a “crazy ambition” yesterday ended in a world record as the British runner Susannah Gill successfully completed seven marathons across seven continents in seven days to win the gruelling World Marathon Challenge in the fastest time by a women athlete.

Along the way Gill, a 34-year-old from London, braved -35C temperatures in Antarctica and 35C heat in Cape Town before finishing the event in Miami in a total time of 24 hours 19 minutes and nine seconds – an average of three hours and 28 minutes per marathon – to beat the previous record by more than three hours.

“It was a crazy ambition but the challenge seemed absolutely irresistible to me,” she admitted. “Ten years ago, I just wanted to get fit and run the London Marathon. Now, marathon running has literally taken me around the world.”

Race organisers warn participants in advance they must be in “excellent health and capable of completing the World Marathon Challenge”. However, fewer than 200 people have completed the annual “777” challenge since Sir Ranulph Fiennes first achieved the feat in 2003.

The €36,000 (£31,500) entry fee, which pays for a chartered plane to fly the participants more than 55,000 miles across the globe, and for accommodation and logistics, is also a big factor in that. But afterwards, Gill admitted the challenge of running successive marathons in Antarctica, Cape Town, Perth, Dubai, Madrid, Santiago and Miami in the space of a week, while having very little sleep, had been tough.

Susannah Gill (@TheIronLadyRuns) I did it!!!! 🏃‍♀️💪



Miami marathon done @WorldMarathon77!!



Finished 777 with a 3:26:24 marathon along South Beach and set a new World Record in the process!!



What a week!! Thank you for all the support along the way and donations to @TeamSportsAid. #marathon777 https://t.co/VvtA8QD7tc

“The first four marathons, I was eating quite well and getting enough calories in, and then marathons five, six and seven I’ve actually been waking myself up because I’ve been so hungry,” she told the BBC.

“I ended up getting an hour’s sleep on one flight because I just had to get up and eat a packet of peanuts, two packets of crisps and a chocolate bar. That became a challenge, because I was burning 4,000 or 5,000 calories a day every day for a week.”

Gill finished second in the first marathon of the event in Antarctica in 3 hours, 53 minutes and 55 seconds but then won the remaining six marathons to take overall victory. Her fastest time, 3 hours, 11 minutes and 49 seconds, in Madrid, was even achieved after a sprint finish.

It was an impressive achievement given that Gill, a leading executive in British horse racing, only started running in 2008 when she entered the London Marathon to get fit. Since then she has run 45 marathons, with a fastest time of 2 hours 58 minutes. But she admitted the intense preparations needed to run seven marathons in seven days had made her rather antisocial.

“It’s been pretty much every weekday after work, and then a standard weekend was either a three-hour run on Saturday and a four-hour run on Sunday, or a three-hour run on Saturday and then go off and race a marathon on Sunday,” she explained. “It doesn’t really give you a lot of time to see friends and family.

“Now I can go back to running just one marathon at a time, which will be quite nice,” she added.