Current practice in three dimensional (3D) part construction and product assembly definition within a digital mock up (DMU) is based on the nominal sizing of geometry. This approach does not reflect real part dimensions when they are manufactured or the assembly conditions as they come together during the final build. The value of virtual assembly planning (VAP) using clash and gap detection is therefore limited to modelling error identification within the computer-aided design (CAD) domain for nominal conditions only. VAP could become a significantly more powerful tool if the 3D representation of components within the DMU were more representative of ‘as manufactured’ dimensions. This paper presents the evolution and validation of an enriched digital mock-up (EDMU) introducing the concept of the hybrid assembly. This enables the representation of components in sizes which can range between upper and lower dimensional limits (in line with maximum and least material conditions) in addition to the nominally defined form. The resulting capability has been exploited to perform early stage tolerance and assembly analysis on a part by part basis within the CAD model by tracking the effects of possible variations in key control characteristics (KCCs) on key product characteristics (KPCs). The approach enables better informed tolerance consideration earlier in the design process as the CAD model / DMU evolves. This has the potential to reduce the time, effort and computational load associated with the application of statistical tolerance analysis methods later in the design cycle.