Several executive estates in the Croydon area were developed in the middle of the 1920s. In 1929, William died: the other two brothers remained in Liverpool and William’s son, Richard Rylandes Costain, was sent to run the London company. Under him, Richard Costain & Sons expanded its housing building large estates all around London, the largest being a site for 7,500 homes in South Hornchurch, started in 1934. Perhaps the best known development of all was Dolphin Square, which was completed in 1937.