The Immigration Act of 1971 was more explicit in its racial underpinnings than its 1968 predecessor. ‘Non-patrials’, or those that did not have a parent or grandparent born in Britain but resided in the Commonwealth, were now termed ‘British Overseas citizens’ or ‘British Dependent Territories citizens’ with no right to settle in Britain. This meant that you could be part of the Commonwealth but not settle in Britain unless you were a ‘patrial’. The Act coincided with growing political unrest in Uganda which raised the prospect of Ugandan Asians with Commonwealth citizenship migrating to Britain.

Check out a House of Lords Debate on the deteriorating situation in Uganda: https://api.parliament.uk/historic-hansard/lords/1972/sep/14/uganda-asians#S5LV0335P0_19720914_HOL_122