Counter-terror police are investigating after a package containing uranium that was seized at Heathrow suspected of being smuggled to Iranian terrorists living in the UK.

The potentially-lethal uranium can be used in a dirty bomb. Police are reportedly targeting an Iran-based firm with UK premises where the material was due to be delivered.

According to a report by The Sun, alarms were set off after specialist scanners in Heathrow’s Terminal 4 detected the chemical, forcing officers to isolate the shipment in a dedicated radioactive room. The package originated from Pakistan, arrived on a passenger flight from Oman and was destined for Iranian nationals in the UK.

A Heathrow source told the newspaper: “The race is on to trace everyone involved with this rogue non-manifested package. Security bosses are treating this with the seriousness it deserves. Protocol was not followed and this is now an anti-terror operation. There are real concerns over what the Iranians living here wanted with non-disclosed nuclear material.”

Strict protocols must be followed to fly dangerous cargo, particularly on passenger flights.

Former commander of the UK’s nuclear defence regiment Hamish De Bretton-Gordon said: “For uranium to turn up on a commercial airliner from Pakistan to an Iranian address in the UK is very suspect.”

“The nuclear threat has never been higher. Higher than it has ever been in the Cold War,” Bretton-Gordon continued.

“The good news is the system worked and it has been interdicted. Uranium can give off very high levels of poisonous radiation. It could be used in a dirty bomb.”

The International Atomic Energy Agency (IAEA) has said Iran possesses more than 60kg of uranium enriched to 60 per cent, which puts it within reach of one atomic bomb.

Significant technical hurdles would then have to be overcome to construct a bomb small enough to fit on a missile. But the UK said that Iran was moving quickly on a potential weapon.

On Tuesday, the Met Police said, “We can confirm officers from the Met’s Counter Terrorism Command were contacted by Border Force colleagues at Heathrow after a very small amount of contaminated material was identified after routine screening within a package incoming to the UK on December 29.

“The material has been identified as being contaminated with uranium.”

Commander Richard Smith, head of the Met’s SO15 counter-terror branch, said: “I want to reassure the public that the amount of contaminated material was extremely small and has been assessed by experts as posing no threat to the public. 

‘’Although our investigation remains ongoing, from our inquiries so far, it does not appear to be linked to any direct threat. As the public would expect, however, we will continue to follow up on all available lines of enquiry to ensure this is definitely the case.

“However, it does highlight the excellent capability we and our partners have in place to monitor our ports and borders in order to keep the public safe from any potential threats to their safety and security that might be coming into the UK.”