I have been trying to remind myself of the architectural history of Buckingham Palace and why it is as it is, a palimpsest.   The answer is that the projecting wings were designed by Nash as part of his lavish and excessively expensive remodelling in the late 1820s, which included Marble Arch facing the Mall between the two wings.   Edward Blore replaced him in 1830.   It was Blore who created the first version of the east front, including the balcony, in 1847, and this was remodelled by Aston Webb just before the first world war.