The incurable brain disease vCJD, the human form of BSE (mad cow disease), may be widespread and advancing undetected, scientists say.

Concerns over the safety of blood transfusion and the use of surgical instruments were raised by the stark warning from researchers at the Institute for Animal Health in Edinburgh today.

So far, 161 people in the UK have succumbed to the fatal infection which slowly destroys the brain. Two cases have been linked to transfusions.

Estimates of the eventual size of the epidemic have ranged up to hundreds of thousands of people, but most scientists hoped that, 10 years after the first cases were identified, we were over the worst.

The new warning will raise pressure on the Government to change the rules on post mortem examinations to include tests for vCJD - which cannot be detected until after death- to determine the extent of the epidemic. A scientific review is under way.