Biosecurity is likely to be seriously compromised by the United Kingdom’s exit from the European Union. Common rules and safeguards, backed by a common judicial system, have for decades protected human, animal and plant health against biological hazards. Even so, ash dieback still threatens 60 million UK trees, and African swine fever has spread to Europe (see I. Capua and M. Monti Nature 566, 326; 2019).

Despite the rush to pass the huge volume of secondary legislation required by the EU Withdrawal Act before the end of this month, it is almost certain that the mechanisms and operational capacities to replicate these protective systems nationally will not be in place (see, for example, go.nature.com/2tislyv). Establishing such mechanisms will take time — and, meanwhile, hazards will persist.

Although we might still exchange information with the EU in response to common threats, we shall no longer be able to access the relevant data systems. Even if we continue to collaborate in research and innovation, our contribution to biological security policies will dwindle. Our voice in strategic decision-making will be silenced.