Thursday's admission by the Ministry of Agriculture that BSE can be passed from mother cow to calf - a proposition it used to dismiss as "rubbish" - is its second such setback in as many weeks, following the discovery that sheep could contract the disease from eating feed made from cows. Together with the explosive announcement last March that eating BSE-infected beef was the likeliest cause of a new strain of Creutzfeldt-Jakob Disease, these discoveries destroy the basis of the Government's policy over the best part of a decade and open up the prospect of an even greater potential hazard to human health.
From the late 1980s, ministers promulgated - no, proseletysed for - a comforting and commercially convenient doctrine, now proved to be scientific nonsense. Cattle got BSE, they insisted with more faith than evidence, solely from eating feed containing remains of sheep infected with scrapie. Even though it had come from sheep, they went on with more hope than logic, the disease could not be passed on to other species who ate the cattle. And, since people had never caught scrapie from eating lamb, they triumphantly concluded, there was certainly no danger from beef.
Wishful thinking thus became political doctrine, presented as scientific fact. Controls were brought in grudgingly and late, and not properly enforced. Those who questioned the doctrine were ridiculed and, sometimes, persecuted. When inconvenient facts emerged, the Government first tried to fit them to the dogma, and, when this proved impossible, announced that they nevertheless did not affect the safety of beef.
This disreputable process continues. Last week's admission finally enabled ministers to come to terms with the increasingly inconvenient fact that more than 28,400 cattle have contracted BSE despite being born after the feed that was supposed to cause it was banned. Even though it has long been known that scrapie was passed down from ewe to lamb - and even though a House of Commons Select Committee recommended, in vain, six years ago, that farmers should not be allowed to breed from the offspring of cows with BSE - they refused to believe that anything of the kind could happen with cows. The calves, they insisted, could only have got BSE from being illegally given prohibited feed.
That improbable explanation has now been blown away by the ministry's own experiments. These found that 10 per cent more of the offspring of infected cows contracted the disease than those born to healthy mothers. But no sooner had the ministry admitted the findings - in an anonymous briefing by officials after Parliament had safely broken up for the holidays - than it was trying to massage them into insignificance. The 10 per cent excess, it said, would actually be only 1 per cent in real farm conditions.
This is sleight of hand. Half the tenfold reduction comes from excluding the 50 per cent of infected calves born male. Slaughtered earlier than their sisters, they would be butchered and eaten before they had time to exhibit the full disease, but while they were nevertheless infected - not a particularly reassuring thought. The rest results from more statistical juggling. The researchers only examined the last calves born to cows before they exhibited BSE. The ministry simply assumed that previous calves from the same cows had not developed the disease - even though it admits that they might have done - and so divided by another five to get their 1 per cent.
The Government's Spongiform Encephalopathy Advisory Committee (Seac) has already cast doubt on this calculation. And it does not fit the figures. Some 160,000 cows have had BSE, and they would have had about 640,000 calves. One per cent of these would amount to 6,400 infected calves; but over four times as many have developed the disease.
The ministry has reason to minimise the figure. If lots of calves are inheriting BSE, it will take far longer to eradicate. The slaughtering policy so painfully negotiated with the EU becomes largely irrelevant. The lifting of the EU beef ban by November, on which John Major has staked his reputation, becomes a pipe-dream.
There are also worrying implications for health, since the calves do not come into contact with their mothers' brains, spinal cords or offal - the organs removed to make beef "safe for human consumption" - and so must have been infected some other way. One possibility is that they got the disease from blood, which of course permeates every butcher's joint.
This latest fiasco has already provoked new calls for the departure of Douglas Hogg, the Agriculture Minister. In itself this would solve nothing. The problem at the ministry stretches back to when Hogg was in short trousers and, on present form, will continue long after he is put out to grass. Part of the trouble is that it is both responsible for regulating the industry and for promoting it - an inevitably disastrous arrangement.
Some senior ministry officials still genuinely, if privately, believe that all would be well if only Seac, which originally sounded the alarm about the risk to people, had kept quiet. They see BSE purely as an animal health problem, point to its falling incidence in cattle and congratulate themselves on a good job. Human health hardly enters the picture, even though they are charged with ensuring food safety. Concerns about pesticides or phthalates in baby milk have run into the same attitude.
Opposition parties have called for an independent Food Safety Agency, which would be an important first step - though not if it reports to the Department of Health, whose record is equally lamentable. But there is an increasing view, as one top Whitehall figure told me last week, that the ministry should "be abolished".
Whitehall insiders frankly describe the ministry as "an extension of the farming lobby" and speak with awe of the "deference" it shows to the National Farmers Union. Yet by letting the BSE crisis get out of control it has already gravely damaged farmers and the food industry.
It may have served its purpose in regenerating British agriculture after the Second World War, but its usefulness is long past. Promoting the agricultural industry should be left to the Department of Trade and Industry. Its sadly abused countryside functions should be attached to the Department of the Environment. Food safety should go to the independent agency. And the ministry, condemned by its incompetence and arrogance, should follow the hundreds of thousands of cows to the slaughterhouse.