A man in his 60s has been arrested on suspicion of a terror offence after traces of uranium were found at Heathrow Airport in December.
It comes after counter-terrorism officers searched an address in Cheshire on Saturday.
The man was arrested under Section 9 of the Terrorism Act 2006, which covers the making and possession of radioactive devices and materials.
He was released on bail until April.
Commander Richard Smith, head of the Metropolitan Police's Counter Terrorism Command, said that "based on what we currently know", the incident "still does not appear to be linked to any direct threat to the public".
He said officers were continuing to investigate to "ensure this is definitely the case".
The search of the Cheshire property had been completed and police said no material that could be a threat to the public was found.
Border Force officers discovered the radioactive material with a shipment of scrap metal during a routine screening on 29 December.
Uranium is an element which occurs naturally. It can have nuclear-related uses once it has been refined, or enriched. This is achieved by the use of centrifuges - machines which spin at supersonic speeds.
Low-enriched uranium can be used to produce fuel for commercial nuclear power plants.
Highly enriched uranium has a purity of 20% or more and is used in research reactors. Weapons-grade uranium is 90% enriched or more.
