Counter-terrorism investigators will “follow every avenue” to discover how material contaminated with a radioactive substance came to be found at Heathrow Airport.

Uranium was detected during routine screening of a package at the airport on December 29, that according to the Sun had originated in Pakistan and arrived on a flight from Oman.

The newspaper reported that the material is thought to have been destined for Iranians based in the UK.

Giving evidence at the London Assembly Police and Crime Committee on Wednesday, Commander Richard Smith, head of the Metropolitan Police counter-terrorism command, said that police will “follow every avenue” to find out the circumstances.

He said: “It’s understandable that a report like this would attract considerable attention and potentially concern.

“The circumstances are that in the course of routine scanning at London Heathrow an element of cargo was identified that was emitting a radioactive signal.

“There are procedures in place to deal with these sorts of incidents and those procedures were enacted.

“As part of that the counter-terrorism commands were contacted and have opened an investigation into the surrounding circumstances.”

He said that the primary concern was whether there was a public health risk, and there was not.

“The consignments that had been identified included a very small amount of contaminated material”, Mr Smith said.

He added: “The amount of material we’re talking about was very small, and there was no threat to public health or public safety identified.

“We will of course, follow every avenue to see what the background to this was and satisfy ourselves that there’s no further threat.”

The BBC reported that the uranium was found in a shipment of scrap metal.

Colonel Hamish de Bretton-Gordon, a chemical and biological weapons expert, told the BBC Radio 4 Today programme that people should be reassured that it was detected.

He said: “It’s very clear that the comprehensive surveillance network that we have in place in this country, run by the security services, the police and others, has actually worked and picked up potentially a very dangerous containment that could provide a threat.

Mr de Bretton-Gordon, the former head of the UK’s nuclear defence regiment, added: “In this country I think people should be pretty reassured that we’re not going to see dirty bombs from this type of material.”

Asked what could have happened to the metal, he said: “If it is for nefarious reasons, for bad reasons, to create mayhem by Iranians or some sort of Russian proxy, then that is an area of concern.

“But I think the key thing is that there are people looking out for this, and this should not worry the public unduly.”