Drawing on the theory of contracts and Schumpeterian models of innovation, we demonstrate that information asymmetry and risk aversion are conducive to effect-size heterogeneity and sub-optimal allocation of R&D subsidies. Utilising an unbalanced panel of 43,650 British firms from 1998 to 2012 and an entropy balancing methodology, we find that R&D subsidies are less likely to generate additionality effects when: (a) firms are larger, older, or more R&D-intensive; and (b) investment in basic research or during crisis episodes is considered. We also report that over 85% of the subsidies are allocated to large, old and R&D-intensive firms that do not deliver additional R&D investment. Our findings reveal a policy conundrum: the case for R&D subsidies is stronger during economic downturns, when R&D investment is in basic research and when firm age, size and R&D intensity reflect success in converting R&D investment into innovative product lines; but the subsidy is less likely to increase business R&D under these conditions.