PARIS - Around one person in 2,000 in Britain carries the protein linked to the human version of mad cow disease, a figure higher than previous estimates, a study said on Tuesday.
But how many people will actually develop the crippling and ultimately fatal disease is unknown, its authors say.
They also warn Britain to fight the risk of wider contamination through blood transfusions and surgical instruments.
The study, published online by the British Medical Journal (BMJ), is the most exhaustive attempt yet to quantify the risk to Britons from variant Creuzfeldt-Jakob disease, or vCJD.
This is a brain-destroying disorder whose suspected cause lies with eating beef contaminated by mad cow disease, a bovine illness that erupted in Britain in the late 1980s and spread to other countries through cattle exports.
Culls to curb mad cow disease - official name bovine spongiform encephalopathy (BSE) - went into higher gear in the 1990s.
But experts have been struggling to calculate the risk for people exposed to the rogue prion protein, called abnormal PrP, during the risk years.
The problem is that little is known about the incubation time for vCJD, although it is likely to be long, and not everyone who carries the prion may develop the disease itself.
Researchers led by Sebastian Brandner, a professor of neuropathology at University College London, analysed 32,441 appendixes that were removed at 41 British hospitals, and tested them for PrP.
Sixteen samples were positive, a figure that, when extrapolated across the United Kingdom's population equates to around one in 2,000.