The British preference of Australian immigration policy was challenged by the demands of a rapidly expanding post-war programme overseen by the newly established Department of Immigration. An essential function of the department was the screening of prospective migrants against criteria shaped by national population policy preferences. This paper examines Australia’s post-war immigration security screening policies in domestic and international contexts. It compares the immigration department’s approaches to immigrating British subjects with their approaches to those from other national and ethnic backgrounds. We explain how assumptions about the free passage of British subjects across empire could persist until the 1970s despite revelations that Australian authorities were powerless to stop those with serious criminal histories gaining entry to the country. These revelations about risky British migrants exposed the limits of Australian control over entry and exclusion, while illuminating the emerging frameworks of post-war border controls.