Hidden under the carpets in the Royal Society's prestigious London headquarters lurks an unpleasant secret.

The inlaid wooden floor in one of the public rooms close to the Wellcome Trust lecture hall sports a border design made up of interlocking swastikas. And these are the real thing: part of the national scientific institute's home in Carlton House Terrace was once the German Embassy.

The floors that bear the Nazi emblem were in a room used by the ambassador to meet dignitaries.

They form a small element of detail in an interior designed by Albert Speer, Adolf Hitler's favourite architect, during the embassy's refurbishment in the late 1930s.

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He was also responsible for the marble staircase, which was made from stone donated by Italian fascist leader Benito Mussolini. It is thankfully free from any symbolism.

Outside the building, by the Duke of York steps, is the grave of the German Ambassador's dog, marked "Giro - a true companion".

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The building was taken over by the Foreign Office after the outbreak of war in 1939 and was stripped of most of its Nazi regalia before being rented out to the Royal Society in 1967.