A man in his 60s was later arrested in northwest England, but has been released on bail, British police said on Sunday.
“Based on what we currently know, this incident still does not appear to be linked to any direct threat to the public,” said Richard Smith, head of the Metropolitan Police’s counter-terrorism unit.
The arrest was made under the UK’s special terrorism legislation. The investigation continues, according to the police.
“The discovery of what was a very small amount of uranium in a package at Heathrow Airport is clearly concerning, but it demonstrates the effectiveness of the procedures and controls in place with our partners to detect this type of material,” Smith said.