The Conservative government did not carry out a legally required assessment of how greenlighting the use of a banned pesticide, described as a “death blow to wildlife”, would affect some of the most important nature sites, documents have revealed.

The previous government gave emergency approval this year for sugar beet farmers to use Cruiser SB for the fourth year in a row.

A single teaspoon of this pesticide is enough to deliver a lethal dose to 1.25 billion bees. In granting approval, the Department for Environment, Food and Rural Affairs (Defra) went against the advice of the Health and Safety Executive and the UK expert committee on pesticides.