Biodiversity conservation policy in agricultural landscapes largely relies on payments that offset the profit losses that are associated with biodiversity-friendly land-use measures. Action-based payments reward the conservation measures directly, while the increasingly promoted result-based payments reward the ecological outcomes of conservation efforts. Result-based payments have been shown theoretically and empirically to be efficient when conservation costs are spatially heterogeneous. Often mentioned as an open issue but not yet addressed in this context is the role of ecological spillover, so that conservation efforts one one farm affect the effectiveness of conservation efforts on other farms. Using a stylised model of two farms, I show that negative spillover (that may arise from the concave species area relationship present in most ecosystems) favours action-based payments and disfavours result-based payments, while positive spillover (that may arise from landscape-scale population dynamics observed in species that are structured as metapopulations) favours both payments but particularly the result-based payment. The effect of asymmetry in the spillover depends on whether the spillover is positive or negative and on how the spillover asymmetry relates to the heterogeneity in the conservation costs.