They are already the youngest Britons to have taken in the infinite views and razor-thin air atop Mount Everest. Their latest venture has been merely to help to save the planet.

Rob Gauntlett and James Hooper set foot back into civilisation yesterday after trekking 26,000 miles into the record books on the first expedition from the magnetic north pole to the magnetic south pole entirely under natural power.

Having hopped 180 degrees from one frozen extremity to another, the 21-year-old explorers were warmly embraced by friends and family in Sydney Harbour, 400 days after setting off on April 8 last year.

“Some people will do anything to get to Sydney,” said Matt Brown, tourism minister of the state of New South Wales, as he greeted the adventurers, who saw land for the first time in 60 days.

During their gruelling expedition, the childhood friends tested their limits on ski, dog sled, boat and bicycle through more than a dozen countries on three continents, including Greenland, the United States, Mexico, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Ecuador, Peru, Chile and Argentina.

The final leg of 8,500 nautical miles (9,780 miles) was completed late last month after sailing on the appropriately named icebreaker yacht Blizzard in minus 50C (-58F) temperatures through unpredictable waters to the magnetic south pole.

“We got knocked down on Blizzard only a couple of weeks ago, which essentially means the mast went underneath the water,” Mr Gauntlett, from Petworth, West Sussex, said yesterday. “The whole world was turned upside down and we were experiencing 80ft waves, so to be here was a real relief.”

The journey was as much about inspiration as perspiration, with the aim of raising awareness about climate change, as well as money for The Prince’s Trust, but it was almost cut short with potentially fatal consequences soon after it began.

While skiing and pulling their supplies between Canada and Greenland, Mr Gauntlett was knocked out as he plunged through melting sea ice. He remained unconscious for four hours and spent a week recovering in a remote hospital.

“I think probably the lowest point of the whole trip was when Rob fell through the ice in the Arctic,” Mr Hooper, from Wellington, Somerset, said.

“He fell through the sea ice and the water temperature was almost minus 2C, so he was unconscious after being in the water for about four minutes before I could get back to him.

“We weren’t sure whether he was going to get through that or not.”

Determined to continue, the intrepid former pupils of Christ’s Hospital in Horsham, West Sussex, then sailed to New York to cycle Chile.

The two set off for the poles less than a year after conquering Everest, aged 19, in May 2006.

Topping Everest and the poles is a tall order, but their next venture is a challenge in its own right: paying back some of the £100,000 debt they have run up on a journey that cost £350,000.

They plan to write a book about their experiences, produce a documentary and tread the corporate speaking circuit.

“It’s a bit of a crazy idea to come up with Everest, but I suppose this has topped that. It’s going to be little bit strange coming back to the UK and thinking about getting a real job,” Mr Gauntlett, who celebrates his birthday today, said.

Homeward bound the pair may be, but Mr Gauntless confesses to still harbouring a slightly smaller-scale ambition: circumnavigating Greenland in a sea kayak.

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