Defra experts are investigating a discovery of the potato disease ring rot at a packing plant in Cambridgeshire.
Workers at the undisclosed plant spotted two Santé variety potatoes that were carrying signs of infection.
The potatoes had come from a large grower in Herefordshire, whose identity is also unknown.
A spokesman for Defra said that it was too early to know whether all potatoes at the farm and packing plant would need to be destroyed.
“We are working now to isolate and destroy the infection,” he said.