Diagnostic models such as the P Indicators Tool have been used to predict the risk of P losses from different areas of agricultural land to watercourses. These models embody the source "mobilization delivery" impact framework as a simple logical summary of process understanding. however, the assessment of P delivery has been neglected in the past. An alternative, decision-tree approach to predict the delivery of P to water bodies is presented here. The approach was developed as part of the DEFRA PEDAL project (http://www.lec.lancs.ac.uk/cswm/projects) and makes use of national coverage data held within a GIS at the 1 km2 scale, in combination with a "field toolkit" of measurements and qualitative observations. For all catchments, monitoring of total P loads in receiving waters has occurred over recent years enabling evaluation of the modelling and field toolkit approach.