European Union member states banned the outdoor use of neonicotinoid pesticides in 2018.
The ban was hailed as a "major victory” by campaigners, as various studies showed the dangers the chemicals pose to bees and other pollinators.
Michal Gove, who was Environment Secretary at the time, supported the ban and said the restrictions would be kept following Brexit.
But the government has since approved the use of one neonicotinoid pesticide to tackle a crop disease affecting sugar beet.
Professor Dave Goulson
Professor of biology Dave Goulson, who specialises in ecology and conservation of bees and other insects at the University of Sussex, described the government's decision as "foolish".