Thousands of patients will have to be warned that they may have been exposed to vCJD (Creutzfeldt-Jakob disease) during their operations in British hospitals.

Doctors in up to 41 hospitals unwittingly operated on people whose bodies were incubating the human form of mad cow disease, before using the same instruments on other people, according to new research.

Experts have warned that even stringent sterilization provides no guarantee that medical instruments will not pass on the disease. Other cases have been documented where patients with a similar disease, sporadic vCJD, underwent brain probes and then passed the condition to others via the instruments, despite the fact that they were repeated sterilized.

Those most at risk from contracting vCJD would have undergone operations on the brain or spine. It is these areas of the body that harbour the greatest concentration of the protein prion that mutates to cause the disease.

Furthermore, at least 22 patients were given blood transfusions with blood donated by people who were later diagnosed with the brain wasting condition.

Health secretary Alan Milburn is expected to announce a move to trace those potentially exposed to the disease in the next few weeks.

He is believed to be concerned however about the impact on people of being told that they may be harboring a deadly disease for which there is no available conclusive test, and no cure.