Wildlife charities have called on the Government to act after leaked documents warned that a pesticide could pose a major risk to bee populations.
A memo from US government scientists revealed that the neonicotinoid pesticide – clothianidin, was extremely harmful to the insects.
The file reveals that some of the tests in the approval process for the chemical were seen as inadequate by scientists as they are unable to detect environmental damage.
Neonicotinoid pesticides are highly toxic to bees and other insects and are used in the UK for agriculture and horticulture production.
Defra insists that the pesticide is not dangerous if used correctly.
The US Environmental Protection Agency (EPA) scientists flagged up the risks to honey-bees and aquatic insects that would result if the US Government approved the request for clothianidin to be used as a treatment on cotton and mustard seeds.
Matt Shardlow, chief executive of Buglife said: "We rely on bees and other insects to pollinate our crops and keep our rivers healthy.
"This leak is yet another warning that the use of neonicotinoid pesticides could be contributing to the current decline in wildlife.
"We have again asked Government to take protective action."
In the leaked memo, the EPA scientists state that "information from standard tests and field studies, as well as incident reports involving other neonicotinoids insecticides suggest the potential for long-term toxic risk to honeybees and other beneficial insects".
It continues: "Clothianidin's major risk concern is to non-target insects (that is, honey bees)."
Clothianidin is a neonicotinoid insecticide that is both persistent and systemic.
A Defra spokesman said: "We already know that there are risks if a product isn't used correctly – and we're glad that this memo reinforces that view.
"We have a robust system for assessing risks from pesticides in the UK that is based on evidence - and current evidence shows that there is not an unacceptable risk to bee health from these products."