According to the latest research far more people may be at risk of contracting variant Creutzfeldt Jakob Disease (vCJD) than previously thought.
vCJD is the human form of Bovine Spongiform Encephalopathy (BSE), also known as Mad Cow Disease.
Scientists at the Institute for Animal Health in Edinburgh say a long incubation period for the disease, coupled with an ability to pass it on through blood transfusions and surgical instruments, has the potential to create a "significant public health issue".
By carrying out studies on mice, the team concluded that vCJD could lie in the body for many years without showing any symptoms.
They suspect a "significant level" of underlying vCJD may already be present in the population.
The experts say the incurable brain disease vCJD, the human form of BSE (mad cow disease), may be widespread and advancing undetected as it can be passed from human to human through secondary transmission - such as blood transfusions and contaminated surgical equipment with ease.
The warning raises fears over the safety of blood transfusion and the use of surgical instruments.
vCJD affects the brain and is believed to be passed from cattle to humans through eating meat infected with BSE.
Some people carry the agent but never show symptoms, while others develop the disease after many years.
The study reveals that people may not know they have the agent for vCJD and therefore there is a risk "of further disease transmission".
To date 161 people in the UK have been victims of the fatal infection which slowly destroys the brain and two of those have been linked to transfusions.
Estimates of the ultimate size of the epidemic have varied from hundreds to thousands of people, but most experts believed that 10 years after the first cases were identified, the numbers would decline.
The warning issued via the new study will pressurise the Government to change the rules on post mortem examinations to include tests for vCJD - which cannot be detected until after death, in order to determine the extent of the epidemic.
A scientific review is currently under way.
The study is published on-line by The Lancet Neurology.