When the Union of South Africa was formed in 1910, the electoral qualifications in use in each pre-existing colony were kept in place.
The first challenge to the Cape Qualified Franchise came with the Women's Enfranchisement Act, 1930 and the Franchise Laws Amendment Act, 1931, which extended the vote to women and removed property qualifications for the white population only – non-white voters remained subject to the earlier restrictions.
In 1936, the Representation of Natives Act removed all black voters from the common electoral roll and introduced three "Native Representative Members", white MPs elected by the black voters of the province and meant to represent their interests in particular.
[1] Mowbray was created in 1929, out of parts of the abolished Liesbeek and Rondebosch seats (the latter would reappear for the very next election), and like the rest of Cape Town at the time, it was loyal to the liberal and pro-British side of South African politics.
He resigned in 1939 to take up appointment as Administrator of the Cape Province, but the seat remained safe for the UP until its abolition.