Current UK cash access monitoring relies on Euclidean distance thresholds that treat infrastructure gaps as the sole determinant of exclusion. This paper develops the Cash and Banking Vulnerability Index (CABVI), integrating network-based accessibility with population vulnerability across 43,914 UK small areas. Using Valhalla routing with OpenStreetMap, we apply differential exponential decay functions for distinct infrastructure types. Demand-side indicators encompass age, health/disability, income deprivation, and digital exclusion derived through geodemographic linkage. Results reveal regional clustering in post-industrial Northern England and Northern Ireland, with substantial intra- urban variation demonstrating that aggregate statistics mask neighbourhood-level disparities, challenging uniform distance-based policy responses.