The British Food Standards Agency has revealed that it found traces of spinal cord in a consignment of beef delivered to a meat plant in the North from the Republic.
Inspectors said the beef, which was in breach of strict BSE controls, had been marked fit for human consumption.
Under European regulations, all meat containing traces of spinal cord should be removed before export in new measures designed to keep infected beef out of the food chain.
A spokesman said the British agency would not reveal the location of the processing plant in the North involved in the breach.