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The safety of the world’s most widely used insecticide has been questioned by a parliamentary inquiry, with MPs accusing regulators of “turning a blind eye” to the risk for bees.

A growing body of scientific evidence has linked the widespread use of neonicotinoid pesticides on crops to a serious decline in the bees and other pollinators, which are vital in producing a third of all food. The inquiry has uncovered evidence, apparently ignored by regulators, that the toxic insecticide can build up in soil to levels likely to be lethal to most insects, including the bees that overwinter in soil.

“European regulators seem to have turned a blind eye to data on the danger that one of the world’s biggest selling pesticides could pose to bees and other pollinators,” said Joan Walley MP, chair of the Environmental Audit Committee (EAC). “Evidence seen by the committee raises serious questions about the integrity, transparency and effectiveness of EU pesticides regulation. Data available in the regulators’ own assessment report shows it could be 10 times more persistent in soils than the European safety limit.”

The insecticide in question is called imidacloprid and is manufactured by Bayer. Prof Dave Goulson, an ecologist at the University of Stirling, said: “The data show unequivocally that imidacloprid breaks down very slowly in soil, so that concentrations increase significantly year after year with repeated use, accumulating to concentrations very likely to cause mass mortality in most soil-dwelling animal life.”

The decline of bees has previously been blamed on starvation as meadows and other habitats are ploughed up, and from diseases and parasites, such as the varroa mite. But a flurry of peer-reviewed studies in 2012 have singled out the harmful effects of neonicotinoids, from making bees lose their way home to failing to produce enough queens. The European Food Safety Authority (EFSA), which assesses the risks of pesticides accepted earlier in 2012 that current “simplistic” regulations contain “major weaknesses”. But the UK government has failed to follow countries including France, Germany, Italy and Slovenia in suspending the use of some neonicotinoids, although it has accelerated its research on the issue.