The government warning late last month that 40 million of the nation's sheep may have to be slaughtered because they had been infected with BSE was unfounded and unnecessary, according to a late-night press release issued by the UK Department for the Environment, Food and Rural Affairs (Defra).

Research that prompted the cull fears appears to have been fundamentally inaccurate. Researchers have long expressed concern that BSE may have spread to sheep, as both species ate infected animal feed before controls were established during the late 1980s and early 1990s.

Laboratory tests have also shown that sheep can be infected with 'mad cow disease' if they are injected with contaminated brain tissue from cattle, but five years of research into the state of the national flock by scientists from the government's BSE advisory committee, Spongiform Encephalopathy Advisory Committee (Seac), there has been little progress.

In the latest round of tests however, scientists at the Institute of Animal Health thought that they were studying sheep brains from the early 1990s. So when they announced the disturbing preliminary findings that the samples were infected with BSE, the government was quick to warn of the "serious implications" should the study be confirmed. Scientists explained that the findings suggested that BSE could be passed from cows to sheep through infected feed, and the disease symptoms misdiagnosed as a similar disease, scrapie.

At the Laboratory of the Government Chemist however, where the samples were sent to make sure no contamination with bovine brains had taken place and distorted the study, it was revealed that the diseased brains had in fact come from cows.

"This cross-checking," admitted Defra's release, "has raised doubts about the validity of the original sample."

The UK's Food Standards Agency responded to the news with a call for more research to establish conclusively whether BSE exists in sheep. The FSA is said to be concerned about the lack of progress at Seac, and is expected to demand better quality research and back a programme to create GM strains of sheep that are resistant to scrapie and other BSE-like diseases. In the meantime however, FSA chairman Sir John Krebs told Radio 4 listeners this morning that there is no reason why the public should not continue to eat lamb.

Elsewhere in the UK media, Defra has been highly criticised for releasing the news of the bungled research so late at night. The Daily Telegraph newspaper accused the government of having "buried" the news at night: "The release was made at a time when it was likely to get minimum coverage. Specialist correspondents were not alerted to its existence.

"It appears, therefore, that the Government was using every trick in the Jo Moore Guide to Gulling the Public to downplay important news of considerable public interest," it added.