During drumlinisation, brecciated bedrock was sheared over the proximal end of a Late Pleistocene drumlin at Kanrawer, western Ireland. High effective water pressures generated by shearing at the ice/substrate interface during this event created a marked proximal-to-distal hydrostatic gradient affecting about 60% of the diamict which forms most of the drumlin sediment pile. This resulted in large-scale sediment reorganisation by Darcian throughflow and closed-conduit flow of expelled pore waters and subglacial meltwater. Proximally, this is reflected in the development of integrated honeycomb gravel structures formed by glaciotectonic shunting and tortuous throughflow in the diamicts. Distally, the honeycomb structures give way to dish and pillar structures, which are connected to gravelly and laminated sandy channel fill facies, which cut obliquely across the long axis of the drumlin. This facies transition reflects throughflow of pore water rising through the sediment pile and expelled along Nye-type channels excavated on the distal drumlin surface. These proximal-to-distal sediment transformations suggest that current theoretical models of drumlin formation do not adequately represent the continuum of subglacial processes which accompany drumlinisation.