"Capital growth becomes income in the year it is realised."
A technicality. Capital growth does never become income because under the law it is not income.
Capital gains are taxed under separate legislation and then collected by the income tax system.
The reason for this? Because the notion of income is an archaic one derived from trust law which basically states that income is the fruit and capital the tree, and I am not joking. As you can see a capital gain is an inherent part of a tree that grew a bit and that you cannot separate without damaging the tree.
