Dr Alistair Forbes Mackay, of the Royal Navy, joined Shackleton's Antarctic Expedition of 1907-09 as a surgeon and was one of the first three men to reach the South Magnetic Pole in January 1909. Along the way, they ate seals and penguins to survive.
Mackay, from Edinburgh, died of exposure four years later on the ill-fated Karluk expedition to explore the regions west of the Parry Archipelago for the Government of Canada, after his ship was stranded, crushed, and sunk by pack ice.
Mackay's Polar Medal and another medal he earned in the Boer War were expected to fetch £3000 to £5000 at Bonhams' Medals and Coin sale in Knightsbridge, London, but a bidding war resulted in one English collector paying £48,000.
The sum was the highest paid at the auction of 325 lots, which made a total of £561,330.
A Bonhams spokesman said: "The wonderful thing about auctions is that when you have a one-off item like this for sale, there is no track record.
"It just takes two people who particularly want it, to knock your estimate out of court.
"We are delighted with the sum achieved by these medals, and with the success of the sale as a whole."