Organic campaigners have criticised the Government for rejecting calls to ban a group of pesticides which they say harm honeybees.

In a letter to the Soil Association, Environment Secretary Hilary Benn said no evidence had been presented to show that “neonicotinoid” chemicals should be banned or restricted because of impacts on bees.

But the organic certifying body said the pesticides damaged the nervous system of honey bees, disrupting their communication, ability to forage for food and flight activity and weakening their immune system.

Use of the chemicals have already been restricted in France, Germany, Italy and Slovenia, the Soil Association said.

Co-operative Farms - the UK's biggest farmer with 25,000 hectares - recently announced a temporary ban on the pesticides on own-brand fresh produce until there is evidence that refutes the chemicals' involvement in the decline of bees.

But the Government said there was no evidence use of the pesticides had led to the falls in the number of bees witnessed in the UK.

And leading bee expert Professor Francis Ratnieks this week said that while pesticides could be a factor in declining numbers of bee hives, the evidence was that they were not important in this country.

Prof Ratnieks, head of the laboratory of apiculture and social insects which was formally launched at the University of Sussex yesterday, said diseases and declines in flowers as sources of food were the main causes of the honeybee's decline in the UK.

The Environment Department (Defra) recently announced £4.3 million of funding for protecting honeybees and research into the threats they face.

Peter Melchett, Soil Association policy director, said: “While new funding and new research are welcome, it will not help if the Government ignores existing scientific evidence that has led other countries to ban chemicals known to kill bees.”

He accused officials of blaming wet weather and inexperienced beekeepers instead of taking responsibility for controlling “bee-killing chemicals” used on farmland in the UK.

But a spokesman for Defra said: “There is no evidence that use of these pesticides has caused the recent declines in bee numbers.

“A number of factors have been identified, including the increased prevalence of the varroa mite, unfavourable weather and the poor management of disease by some less experienced beekeepers.

“The UK has a thorough and robust system of regulation and approval for pesticides, which many farmers use to produce affordable, high-quality food for consumers, and there is no evidence to support increased restrictions.

“We always keep these matters under review, and if there is evidence of an unacceptable risk to bees we will take action.”

Bees play an important role in agriculture, with the value of commercial crops that benefit from bee pollination estimated at £100 million to £200 million a year.

Honey is worth some £10 million to £30 million.