Police said an evacuation of a residential area in Derbyshire is "purely a precaution" after a potentially volatile substance was found in a flat.
A 55-year-old man has been arrested.
Superintendent Paul Markham, who is in charge of the operation, said:
We are not looking for anyone else in connection with this matter and we are hoping that people will not be inconvenienced for too long.
The evacuation is purely a precaution to ensure everybody's safety and residents will be allowed back home as soon as possible.
More top news
Uplifting messages greeted commuters on the London Underground a day after the terror attack in Westminster.
Faith leaders from across London say religious communities will "stand together" in the wake of the Westminster terror attack.
Pc Keith Palmer was among the three people killed yesterday in the Westminster terror attack.