European food safety experts have angered farm leaders by recommending that restrictions to protect consumers from BSE-infected sheep should remain in place - despite being unable to find any evidence of the disease in the national flock.

A 44-page risk assessment by the European Food Safety Authority concedes that BSE has not been found in sheep, even though 1.5 million animals have been tested.

But it remains cautious because sheep have been infected under laboratory conditions. Using this model, the assessment argues that as many as 1 in 20,000 sheep could have BSE.

A similar report by an independent group of UK government advisers concluded that the risk of BSE in sheep was either zero or very low, if present at all.

The NFU described the European assessment as unhelpful. Implementing its recommendations could add additional cost into the supply chain, further devaluing lamb and undermining consumer confidence, it warned.

NFU livestock chairman Thomas Binns said: "We need to make clear that an inordinate amount of time and money has been spent trying to establish whether BSE is present in sheep and at the end of the day they have found nothing."

Under laboratory conditions, it was probably possible to infect an animal with any disease, said Mr Binns. But control measures should be based on the best scientific evidence and actual farming practices.