Formerly, men not wearing military uniform wore knee breeches of an 18th-century design. Women's evening dress included obligatory trains and tiaras or feathers in their hair (or both). The dress code governing formal court uniform and dress has progressively relaxed. After World War I, when Queen Mary wished to follow fashion by raising her skirts a few inches from the ground, she requested a lady-in-waiting to shorten her own skirt first to gauge the king's reaction. King George V was horrified, so the queen kept her hemline unfashionably low. Following their accession in 1936, King George VI and his consort, Queen Elizabeth, allowed the hemline of daytime skirts to rise. Today, there is no official dress code. Most men invited to Buckingham Palace in the daytime choose to wear service uniform or lounge suits; a minority wear morning coats, and in the evening, depending on the formality of the occasion, black tie or white tie.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What century were men's knee breeches forbidden at Buckingham?
unanswerable