The intensity and distribution of deformation within cores recovered from 24 Britannia Field wells has been quantified and used to assess the sub-seismic deformation present. Structural logging has been amalgamated with microstructural and petrophysical analysis of fault rocks and the results used to construct models of the fluid flow behaviour of fault zones and to evaluate the correlations between core-scale structures and the larger-scale seismically mapped fault arrays. Deformation within Britannia is controlled primarily by (1) early sediment disruption, dewatering, detachment and folding in semi-lithified sediments and (2) more long-lived clustered arrays of small faults developed within fault damage zones. Fault population analysis illustrates that seismic-based mapping alone does not provide a good platform for accurately predicting the number of sub-seismic faults present. Analysis of the effect of deformation features on fluid communication highlights the importance of small-scale faults in enhancing communication in complex and initially separate sand bodies.