A man has been arrested in Dundee on suspicion of offences under the Terrorism Act.
The 31-year-old, from Goole in East Yorkshire, was detained and then transferred to West Yorkshire for questioning by counter-terrorism officers.
He was the second person detained in connection with the discovery of "potentially explosive materia
l" at a house in Goole.
However, a police source said the arrests did not concern Islamic terrorism. He said: "This is nothing to do with AQ [al-Qaeda], but it is about extremism."
The 31-year-old man was detained in Dundee in the early hours, a Humberside Police spokeswoman said.
Another man, also 31, was arrested last Wednesday after police seized the unidentified material during a house search in the centre of the East Yorkshire town. Police sealed off the area around the house during the searches and tests are being carried out on the material.
The men, who both come from Goole, have not been named. They were detained under the Terrorism Act 2000 and are being questioned at a West Yorkshire police station.
"We would ask people to go about their business as usual," a police spokeswoman said. "However, we would always urge people to remain vigilant."
Police stepped up patrols earlier this year after two car bombs were found in central London and a Jeep was rammed into a terminal at Glasgow Airport.
The security service MI5 rates the current threat of a terrorist attack as "severe" which is the second-highest level. That means an attack is thought to be "highly likely" according to security experts.
