By Alex Kirby BBC News Online environment correspondent

The UK scientists who carefully examined cows' brains believing they came from sheep are now the object of scorn.

Years of work to see whether sheep could have contracted BSE (mad cow disease) have been undermined, perhaps completely ruined.

But distinguishing the brains of the two species in the laboratory is far from easy.

Even so, the episode raises questions about how crucial research is conducted.

As the armchair scientists jeered, the BSE researchers at the Institute for Animal Health admitted that their study of 3,000 brains had been looking at bovines, not ovines. But their mistake would not have been obvious.

Missing paperwork

Peter Jinman is a vice-president of the British Veterinary Association (BVA), and a member of the Spongiform Encephalopathy Advisory Committee (Seac), which advises the government on BSE and related diseases.

He told BBC News Online: "It's a very simple mistake to make when you've got the brains stirred up in a soup, macerated for experimental use. They weren't whole brains.

Any risk from sheep remains unknown

"There's a deep and careful audit going on at the institute, though, because this shouldn't have happened.

"A paper trail should accompany any sample all the way, so clearly something has gone wrong."

The institute's director, Professor Chris Bostock, says the government's Veterinary Laboratory Agency (VLA) told him it had wrongly assured him last December that the brain samples were not contaminated with cow tissue.

Mr Jinman said: "The jury is out on the VLA, but two points are clear.

"Everyone involved in this is as sick as a parrot. And we've still got to get proper answers to the questions we were hoping the research would answer.

"If the research had been sound, and if it had concluded that sheep had been infected with BSE, that would not necessarily have meant the destruction of every sheep in the UK.

Relative risks

"We'd have had to discuss the extent and implications of the problem. But killing the entire national flock is way beyond that - the ultimate point.

"With food safety it's nonsensical to talk of completes and absolutes. Everything in life carries a risk.

Brain samples would have been like a soup

"It's a question of weighing the risk and letting people know what's involved.

"But it's right to raise the question of how we do research in the UK. The key thing is that we do not deride the scientific base of research, or run it down.

"We must try to improve the communication of what science can achieve and what it can't. I sometimes think politicians and the public expect more than it can deliver."

The VLA is an agency of the Department for Environment, Food and Rural Affairs (Defra), and reports to the Environment Secretary, Margaret Beckett, who is answerable to Parliament for it.

The Institute for Animal Health is an independent organisation. It receives an annual grant from the Biotechnology and Biological Sciences Research Council (BBSRC) to support staff, facilities and strategic research.

It is accountable to the BBSRC for the use of the grant. It also competes for government and private sector research contracts. On the BSE study, it is accountable to Defra and Seac.