The ricin may have been in the house for up to two years, police said
A father and son are being questioned by anti-terrorism officers following the discovery of the poison ricin at a house in County Durham.
The find is connected to a police inquiry into alleged extreme right-wing activity.
Ian Davison, 41, and his son, Nicky, 18, were arrested on Tuesday in raids at their homes in County Durham.
The ricin, said to be 6,000 times more toxic than cyanide, will be analysed at the Porton Down government laboratory.
Police have halted their search of Mr Davison's home in Myrtle Grove, Burnopfield, until tests on the substance, found in a sealed jam jar, have been completed.
The former pub DJ's son was detained at his home in Annfield Plain on suspicion of inciting racial hatred but is now also being held under the Terrorism Act.
It is understood his father is being questioned by Durham officers and the North East Counter Terrorism Unit at a police station in West Yorkshire.
Assistant Chief Constable Michael Barton, of West Yorkshire Police, said the poison had been kept in a kitchen cupboard "apparently for up to two years".
Initial testing took place on Thursday at a government facility in Edinburgh.
Mr Barton said it would now be taken to the Ministry of Defence labs at Porton Down, adding: "That transfer will take place under a police or military escort and their report should be finalised in the next few days."
He said the advice of scientists was taken before deciding there was no need to evacuate immediate neighbours of the property.
"I would again like to reassure people in Burnopfield that the substance found was sealed in an airtight container prior to its removal.
"As such no one is believed to have been exposed to the substance or be at risk of any potential ill-effects. We do not believe that there is any risk to public health," he said.