Embossed with the Royal cypher and the title "Prime Minister", the dispatch box was delivered to Thatcher on a daily basis, containing cabinet, foreign and Commonwealth documents for her attention.
It vastly exceeded its estimate of 3,000-5,000 pounds, attracting a round of applause in the auction room when it sold yesterday.
It was among 150 items belonging to the late Conservative party leader known as the "Iron Lady" being auctioned by Christie's auction house with bids pouring in from as far away as the US, Australia and South Korea.
Thatcher, who died on April 8, 2013, at the age of 87, was Britain's only woman prime minister and held office from 1979 to 1990.
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A signed typescript of her famous speech reciting the words of St Francis of Assisi, "Where there is discord, may we bring harmony," sold for 37,500 pounds.
She gave that speech outside No 10, Downing Street shortly after becoming prime minister in 1979.
An online auction of another 200 items belonging to Thatcher closes today.