Methodologies are required to help identify soils that are vulnerable to both suspended sediment (SS) and phosphorus (P) transfer in land run-off to combat the adverse impacts of agriculture on water quality. A laboratory test that quantifies dispersed particles and associated P in the same suspension was developed to estimate the potential mobilization of SS and P due to rainfall impact from 26 European soils with varied soil physical and chemical properties and P inputs. The test recovers an aliquot of the clay and fine silt (<20 μm) fraction of soils after gently shaking in distilled water for 1 min at a 1:50 soil-to-solution ratio and measures the dry residue, total P and dissolved (<0.45 μm) P content. The results of the test correlated well (r2 = 0.7–0.8) with the amounts of SS, total P and dissolved P in overland flow generated by indoor simulated rainfall (intensity 60 mm h−1 for 30 min and a 5° slope). Variation in SS and particulate P mobilization was linked to soil pH, organic matter (or clay) and sesquioxide content, although a multiple regression analysis showed these factors accounted for no more than 55% of this variation. Ranking showed that the soils generating the most sediment did not necessarily generate the most P loss due to variable degrees of P enrichment of the particulate fraction and variable contributions of dissolved P. Particulate P enrichment was related weakly (r2 = 0.5) to soil total P, while dissolved P fractions were predicted well (r2 = 0.8–0.9) by conventional soil P tests (water and Olsen). The environmental soil test has a potential role in identifying the comparative risk of sediment and P mobilization from critical source areas connected via both surface and subsurface pathways, and in providing data for incorporation into models predicting sediment and P transfer at the field and catchment scale.