Repeated attempts by shadow ministers over several years to get access to the documents - which they are convinced contain a "smoking gun" proving complicity between the government and the meat industry - have been rebuffed. But they quote a meat industry spokesman as saying: "The basic motive was profit."
The last Labour government drew up draft regulations in 1978 to stop cattle being fed meat from sheep contaminated by scrapie - now thought to be the cause of the BSE epidemic. But it fell before they could be implemented, and the incoming Thatcher government jettisoned them as part of its drive to relax regulations on industry.
Mr David Clark, the present shadow defence secretary - who spent years trying to probe the reasons for the change as Labour's agriculture spokesman in the late 1980s and early 1990s - told the Independent on Sunday yesterday: "Somewhere buried in Whitehall is the smoking gun which proves the Thatcher government's responsibility for this disaster. All our attempts over many years to unearth it have been frustrated by ministers and their officials."
He said that the Labour government "was alerted just before it left office to the fact that technology in the rendering industry was changing".
The industry, which processes animal parts to be used as feed, was lowering the temperatures at which it operated and using fewer solvents to treat the meat. Mr Clark says Labour feared that this would result in cattle being given feed dangerously contaminated with scrapie.
Labour published draft regulations to prohibit any process that did not kill "disease organisms". But after the 1979 election, Agriculture Ministry documents show, Mrs Thatcher's government favoured new arrangements which "reflected the wish of ministers that in the present economic climate the industry should itself determine how best to produce a high quality product".
It did this in defiance of a warning by the Royal Commission on Environmental Pollution that feeding animal protein to cattle involved "the risk of transmitting disease-bearing pathogens to stock and thence to humans".
In a House of Commons debate in May 1990, David Clark quoted the United Kingdom Renderers as saying: "The original proposals were very expensive, but there was a distinct change of heart when the Conservatives came to office."
Mr Clark then accused the Conservatives government of "following their usual practice of rewarding their friends, including those in the rendering industry".
Mr John Gummer, then Minister of Agriculture, replied in an uncanny echo of last week's ministerial pronouncements: "The absolute priority for the government is public health and the safety of the consumer."Reuse content