A virus threat to sugar beet crops has sparked an emergency authorisation for farmers to use a controversial pesticide - which was banned over fears it could be killing bees.

For the third year running, the government has approved the temporary use of a neonicotinoid seed treatment on sugar beet crops - most of which are grown in East Anglia.

The chemicals were banned by the EU in 2019 due to their potential impact on the health of bees and pollinators.

But this year's threat from the devastating beet disease virus yellows, carried by infected aphids, has prompted the tightly-controlled temporary approval to protect an industry which supplies more than 60pc of the UK's sugar.

Defra's announcement was met with relief from farmers but provoked anger from environmental groups who said the "incredibly brazen" move went against government commitments on pesticide reduction.

Friends of the Earth campaigner Sandra Bell said: "This is the third consecutive year that the government has gone directly against the advice of its own scientific advisors with potentially devastating consequences for bees and other vital pollinators.

"The government must fulfil its duty to protect wildlife and keep pesticides off our crops for good – that means supporting farmers to find nature-friendly ways to control pests."

But Fenland grower Michael Sly, chairman of the National Farmers' Union's sugar board, was "relieved" by the decision.

"The British sugar beet crop continues to be threatened by virus yellows disease, which in recent years has caused crop losses of up to 80pc," he said. "The home-grown sugar industry is working hard to find viable, long-term solutions to this disease."

Defra said strict conditions would be in place and the pesticide, named thiamethoxam, will only be authorised if independent modelling predicts a yellows virus incidence of 63pc or above - much higher than last year's 19pc threshold.

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The decision was informed by advice from the Health and Safety Executive (HSE), the independent UK Expert Committee on Pesticides (ECP) and Defra's chief scientific adviser, Prof Gideon Henderson.

Farming minister Mark Spencer said all criteria had been met for the emergency authorisation and, taking into account the strict controls and mitigation measures, "the potential risks of authorisation (including potential risks to bees) are outweighed by the benefits of use in these circumstances".

But the ECP did not support the application "as potential adverse effects to honeybees and other pollinators outweigh the likely benefits".

Sugar beet is a non-flowering crop, but the HSE acknowledged a "potential concern" arising from bees foraging on pollen and nectar from flowering crops following the treated sugar beet crop.

But gven the rate the chemical breaks down in the soil, it was deemed to be below the levels required for chronic toxicity as long as no flowering crops were planted in the same field for at least 32 months.

The UK's decision comes just days after the EU Court of Justice ruled that member states could not offer exemptions to the EU's ban on crop seeds treated with neonicotinoids.