FARMERS must dread each new despatch from the laboratory. Scientists are now suggesting that BSE could be transmitted back to sheep. Any risk is said to be tiny, but it is potentially devastating nevertheless.

The discovery could yet prompt the total collapse of sheep farming. Eating lamb would be banned. Millions of animals would be slaughtered. Yet more farmers would be sent into bankruptcy. The fragile recovery of our meat export business would collapse as British produce was again shunned by the rest of the world.

This is the worst case scenario. But it is one of two options apparently being considered by ministers should BSE be confirmed in the sheep flock. The other is to allow only meat from sheep genetically immune to BSE to go on sale. This would still entail a mass destruction of livestock.

Two major considerations impinge on these contingency plans, one scientific the other political.

Biologically, the symptoms of the relatively common disease of scrapie in sheep are very similar to those of BSE. That would make it very difficult to determine the scale of any BSE outbreak.

Politically, this news breaks only days after the publication of a damning report into the handling of the BSE crisis. It confirmed that ministers misled the public, playing down the threat with tragic results.

A video of a teenage girl dying from new variant CJD, the human form of BSE, moved the Prime Minister and the rest of the nation. And now we learn the Government has doubled its estimate of the number who may die of the disease.

In such an atmosphere, ministers would feel compelled to take the most drastic action to tackle sheep BSE, however small the risk.

The instinct to protect public health, whatever the cost, is the right one. But that is no comfort for the farmers. They can only wait and hope that BSE in sheep stays in the laboratory and away from the farm.