BBC News - Daniel Sandford
Police are investigating after metal contaminated with uranium was found at London's Heathrow Airport last month.
Officers of the Metropolitan Police's Counter Terrorism Command responded to the security alert which was triggered on 29 December.
The Sun, which first reported the news, said the uranium came from Pakistan.
One line of inquiry is whether it was the result of "poor handling" in the country, the BBC was told. Police say there was no threat to the public.
It was found in a shipment of scrap metal, a source said.