Twilight of the Anthropocene

Phenomenal question.

Like IRL in 1945, the Raj of Sarawak has a microscopic White population, mostly composed of British expats and more importantly the Brooke dynasty.

The demographics of Sarawak are complex and multiracial, with a large youthful population and new arrivals of all kinds ...

The title. Aprox. how much/what section of the population is of British descent or is it just limited to the Brooke dynasty? Is there a sizeable japanese population on the Raj?