They knew the plant in Raynesway, Derby, made propulsion systems for nuclear submarines - but the delicate operation of processing highly-enriched uranium had been classified until now.

Local councillor John Ahern, whose ward covers the plant, promised to investigate reports of serious safety flaws at the factory.

He said: "I am extremely concerned, but let me say that if there has been a breach in safety I will address the issue.

"I owe it to my constituents, the people of Derby, and the workers, to get to the bottom of this. I will be speaking to the powers that be to discover just what has happened."

He added: "There are some serious questions that need to be asked. I am sure the people living near here will be equally concerned.

"We need to seek clarification that this area is safe and that there are not any health problems as a result of this."

Shoppers at Derby's Asda supermarket said they were surprised and worried by the discovery.

Mother-of-two Alison Jones, from Allenton, said: "It is very worrying, especially after what has happened in Japan. We need to know what is happening."