This paper describes the findings of an assessment related to the nature and impact of slope instability for 20 km of chalk cuttings on the Metropolitan Line, and which forms an integral element of London Underground Ltd’s Earth Structures Management Strategy. A desk study and detailed geomorphological field mapping were utilized in order to develop a comprehensive classification scheme for the chalk cuttings. The classification depends primarily on cut-slope geometry and proportion of superficial deposits found in the slope. Restrictive thresholds were identified between classes that controlled the type of instability hazards present. The relative risk to the track was assessed which enabled targeting of future remedial measures to the most appropriate locations and the development of a cost-effective maintenance strategy.