BSE affects nearly all herds

More than 90 per cent of Britain's 9 million cows belong to a herd which has had a clinical case of BSE, or mad cow disease, in the past eight years, according to new calculations by Stephen Dealler, an independent scientist. Other research, by Nick Short at the University of Reading, suggests that BSE could persist in British cattle until 2010 - far longer than the Government has claimed in its negotiations with Brussels.

The result of the first findings is that if Britain regains permission to export cattle from BSE-free herds - one of the main political aims of Douglas Hogg, the Minister for Agriculture, in his battle with the European Commission - it would barely begin to help the beef export business to recover.

Last year the EU ban on British beef effectively killed off the pounds 500m export market. But because so few cows belong to herds which have been BSE-free, the economic impact of restarting exports would be minimal.

More than 160,000 cases of BSE have been recorded in British cattle, and calculations last year by a team at Oxford University suggested that another 700,000 infected animals would have entered the food chain between 1986 and 1995.