The Oratory at Brompton is one of the most splendid churches in London, and by far the most impressive of all those in the metropolis belonging to the Roman Catholics. It is situated in the Brompton Road, east of the South Kensington Museum. Italian Renaissance in style, the church of the Oratory is remarkable for its superb marble columns and altar rails, its vaulted dome, its mosaics, and its carvings in wood and stone. The Lady Chapel, however, is its chief glory here the altar and reredos, inlaid with precious stones, are said to have cost at least £12,000. When the façade is completed, and the interior walls are all hidden, the Oratory will have still greater claims upon general admiration.
source: The Queen's London : a Pictorial and Descriptive Record of the Streets, Buildings, Parks and Scenery of the Great Metropolis, 1896