More importantly, it extended the restrictions of the earlier act to apply to British citizens (termed Citizens of the United Kingdom and Colonies) so that the Act restricted the future right of entry into that part of the territory of the British Realm that lay within the British Isles (ie., the United Kingdom), previously enjoyed by all Citizens of the United Kingdom and Colonies, to those born there or who had at least one parent or grandparent born there.

[3] It was introduced amid concerns that up to 200,000 Kenyan Asians, fleeing that country's "Africanization" policy, would take up their right to reside in the UK (ethnic-Indians in British African colonies had been permitted to retain British citizenship to avoid them becoming stateless should they be denied the citizenship of their newly-independent nations - newly independent Uganda would also expel ethnic-Indians).

The bill went through parliament in three days, supported by the leadership of both the governing Labour and main opposition Conservative parties, though opposed by some Labour backbenchers, a few Conservatives such as Iain Macleod and Michael Heseltine, and the small parliamentary Liberal Party.

Home Secretary James Callaghan had made the proposal for emergency legislation at a special cabinet committee on 13 February 1968.

The minutes noted the bill "might be presented as the government giving way to racial prejudice".