A man has been arrested after explosive materials were found at a property in Gwithian, Cornwall.
Officers from the Major Crime Investigation Team discovered composite chemicals, magnesium ribbon and igniter cord at the house on Wednesday night.
Bomb disposal experts secured the scene and are carrying out further searches.
The 29-year-old local man is in custody at Camborne police station. The arrest is not believed to be linked to recent explosions in other parts of the UK.
A spokesman for Devon and Cornwall Police said: "Found at the address were composite chemicals which, when mixed together, formed explosives; together with magnesium ribbon and igniter cord."
The man has not been identified and police said they were not linking him to the seven letter-bombs in padded envelopes which have been posted to businesses in the past three weeks.
Police are urging companies and organisations to be alert to suspicious packages and to take care when handling mail.
Speculation has focused on angry motorists or animal rights activists, although police say the packages do not point clearly to one group or cause.