A man in his 60s, held on suspicion of terror offences over the incident, has been released on bail.
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, Scotland Yard said.
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.
He was released on bail until April.
Commander Richard Smith, head of the Met’s Counter Terrorism Command, said: “The discovery of what was a very small amount of uranium within a package at Heathrow Airport is clearly of concern, but it shows the effectiveness of the procedures and checks in place with our partners to detect this type of material.”
He said that despite the arrest, and “based on what we currently know”, the incident “still does not appear to be linked to any direct threat to the public”.
But he said officers were continuing to investigate to “ensure this is definitely the case”.