East Anglia's sugar beet growers have rejected accusations that they are "secretly" lobbying the government to allow the temporary use of banned pesticides on disease-ravaged crops.

In response to "unprecedented" crop damage from virus yellows disease, the National Farmers' Union (NFU) submitted an emergency application for the use of neonicotinoids - pesticide chemicals banned due to fears over their impact on the health of bees.

The NFU's sugar board (NFU Sugar) asked growers to support the application to use treated seeds in 2021 by signing a letter to Defra secretary George Eustice. But it added: “We’d ask that you refrain from making this letter public – we believe it will have a stronger impact on the secretary of state if kept out of the public domain.”

Author and environmentalist George Monbiot accused the NFU of secretive lobbying, adding: "This letter tells me very clearly that the NFU is trying to prevent us seeing the lobbying activity it is pursuing. That, to me, is completely illegitimate. If you are lobbying, if you are going to launch a petition, you should do the whole thing in the public eye."

But the NFU said the application was widely reported in the national farming press three weeks ago, and that the letter was targeted specifically at sugar beet growers who, like farmers in other EU countries, wanted the option of using the chemicals in a "limited and controlled way" to control virus-carrying aphids on the non-flowering crop.

Fenland sugar beet grower and NFU Sugar chairman Michael Sly said: "The application was not made in secret, in fact it was reported upon in the media three weeks ago.

“The emergency use application is made under EU legislation and is similar to those granted in other EU countries and is unrelated to Brexit or future UK regulations. The seed treatment would only be used if and when the threat of virus yellows disease in 2021 is independently judged to meet the scientific threshold for action.

“Because of the specific nature of the application, which relates solely and specifically to sugar beet, only sugar beet growers were invited to sign this letter explaining the terrible impact the virus is having on their crops. This was the reason the letter was not forwarded or circulated to a wider group."

Mr Sly said some growers are seeing yield losses of up to 80pc due to virus yellows, adding: "There are currently no other effective protections against this disease and there are serious concerns about the future viability of home grown sugar as a result."