A grim crop virus forecast has triggered a temporary emergency authorisation for East Anglian farmers to use a controversial banned pesticide this year.

Sugar beet growers will have access to seed treated with neonicotinoid chemicals in 2024 after scientists predicted a high risk of virus yellows infection, based on a burgeoning aphid population.

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

But the continuing threat from the devastating beet disease virus yellows - carried by infected aphids and capable of halving beet yields - prompted the sugar industry to seek a temporary derogation.

In January, for the fourth year in a row, Defra agreed a conditional emergency authorisation to use a neonicotinoid pesticide called Cruiser SB - but only if a virus threshold of 65pc was reached.

Now the Norwich-based British Beet Research Organisation (BBRO) has confirmed that the 2024 Virus Yellows Forecast of 83pc has exceeded that threshold, triggering the authorisation.

Defra's conditional authorisation sparked outrage from environmental campaigners, who say the chemicals are "lethal" to bees and harmful to British ecosystems.

Barnaby Coupe, land use policy manager at the Wildlife Trusts, said it was a "deathblow for wildlife and a betrayal of farmers who are producing food sustainably."

But farmers and processors at British Sugar said it was a necessary step to protect beet crops, with any use of the treated seed being subject to strict controls, including limits on the amount used and restrictions on flowering crops being subsequently planted in the same field.

Defra said emergency pesticide authorisations are only granted for a limited time in circumstances "where there is a danger that cannot be contained by any other reasonable means".

Sugar beet plants are harvested before they flower so it says there is "little risk arising from bees foraging on pollen and nectar of the sugar beet crop".

The BBRO says the forecast predicts the proportion of the crop which is expected to show virus yellows symptoms "in the absence of any control measures". 

Last year, the seed treatment was applied to 60pc of the national sugar beet crop, after a 67.5pc virus forecast exceeded the 63pc threshold set for 2023.