between 1962 and 1971, as a result of fears about increasing immigration by commonwealth citizens, the uk gradually tightened controls on immigration by british subjects from other parts of the commonwealth, which included cukcs without familial or residential ties to the uk. the immigration act 1971 introduced the concept of "patriality", by which only british subjects (i.e. cukcs and commonwealth citizens) with sufficiently strong links to the british islands (e.g. being born in the islands or having a parent or a grandparent who was born there) had "right of abode", meaning they were exempt from immigration control and had the right to enter, live and work in the islands. the act, therefore, had "de facto" created two types of cukcs: those with right of abode in the uk, and those without right of abode in the uk (who might or might not have right of abode in a crown colony or another country). despite differences in immigration status being created, there was no "de jure" difference between the two in a nationality context, as the 1948 act still specified one tier of citizenship throughout the uk and its colonies. this changed in 1983, when the 1948 act was replaced by a multi-tier nationality system.