Biodiversity compensation policies have emerged around the world to address the ecological harms of infrastructure expansion, but they have historically experienced weak compliance. The English government is introducing a requirement that new infrastructure developments demonstrate they achieve a Biodiversity Net Gain (BNG). Previous research has highlighted governance gaps that risk undermining the policy’s ecological outcomes and explore the risks caused by capacity constraints in regulators. However, the magnitude of their effects on the policy’s potential biodiversity impacts remains unexplored. We collated BNG information from all new major developments across six early adopter councils from 2020–2022. We quantified the proportion of the biodiversity outcomes promised under BNG which are at risk of non-compliance, explored the variation in strategies that developments use to meet their biodiversity liabilities, and quantified the occurrence of simple errors in the biodiversity metric calculations. Large developments and energy infrastructure are more likely to meet their liability within their own development footprint, and small developments more likely to purchase offsets. We estimate that 27% of all biodiversity units fall within governance gaps that expose them to a high risk of non-compliance. Ideally, more robust governance mechanisms would be implemented to cover on-site biodiversity unit delivery. Alternatively, more of these units could be delivered through the off-site biodiversity offsetting; in the latter case, we estimate that the demand for offsets could rise by a factor of four, increasing the financial contributions generated by BNG for conservation activities on private land. Lastly, we find that 21% of applications contained a simple recurring error in their BNG calculations, half of which have already been accepted by councils, hinting at under-resourcing in councils assessing developments. Our findings demonstrate that resourcing and governance shortfalls risk undermining the policy’s effectiveness at halting biodiversity loss and require addressing to ensure the policy benefits nature.