In the face of rapid urbanisation, increasing diversity of the human condition, ageing populations, failing infrastructure, and mounting evidence that the built environment affects health and well-being, the existing built environment still fails to meet the needs of people with disability. Nevertheless, in something of a parallel universe, improving built environment ‘sustainability’ performance, via measurement, receives much contemporary attention, and analysing the built environment at micro-scale (buildings), meso-scale (neighbourhood) and macro-scale (city-wide) is undertaken from various multidisciplinary perspectives. But, although built environment performance is already measured in many ways, and community inclusion is considered essential for health and well-being, accessibility performance for people with disability, at neighbourhood scale, is rarely considered. The institutional and medical models of disability help explain the inaccessibility of the existing built environment. On the other hand, the social and human rights models of disability offer insight into improving the accessibility of the existing built environment for people with disability. However, ‘disability’ and ‘built environment’ tend not to mix. People with disability continue to experience lack of meaningful involvement in research, participation in decision-making, partnership equality, and direct influence over policy, with the built environment arena increasingly becoming a private-sector activity. The actors involved, however, have little understanding of either the accessibility needs of people with disability, or the inaccessibility, particularly at neighbourhood scale, of the existing built environment. It is in this context that this paper explores the design, planning and politics of an inaccessible built environment, concluding that assessing the built environment accessibility performance for people with disability, at neighbourhood scale, is an essential component in the process of built environment accessibility improvement. Requiring collaboration between the built environment and disability knowledge domains, a new tool measuring neighbourhood accessibility, the Universal Mobility Index (UMI), has emerged and is undergoing further development.