Sergei Skripal and his daughter may have been exposed to the nerve agent used in their attempted assassination through the Russian spy’s car ventilation system, intelligence sources have told a US television channel.
ABC News said sources had told it that intelligence officials “now have a clearer picture of just how the attack was conducted”.
Agencies reportedly now believe the toxin - identified as a fourth generation nerve agent called Novichok - was used in a “dust-like powdered form” and that it circulated through the vents of Colonel Skripal’s BMW.
ABC News, citing three intelligence officials, said that the Novichok agent had been delivered in a powdered form.
“It is a Cold War substance, something they [Russia] claimed never to have,” an intelligence official told ABC News.
The US news channel said that claims that Skripal was angry - he allegedly had been shouting and “acting incoherently” - in a pizza restaurant before his collapse was consistent with the early stages of exposure to a nerve agent.
Boris Johnson has claimed that Britain has evidence from within the last decade that Russia has been “creating and stockpiling” the Novichok nerve agent used in the attack.
Moscow has long insisted that the production of chemical agents stopped in 1992 and that its stockpile of material was completely destroyed by 2017.
But Mr Johnson, the Foreign Secretary, said the UK had evidence “within the last 10 years” that Russia had been making such nerve agents and investigating how to use them for assassinations.
Mr Johnson’s claims came in response to comments made by Vladimir Chizhov, Russia’s ambassador to the European Union, who insisted “Russia had nothing to do” with the poisoning of the former double agent and his daughter.
Mr Chizhov also risked the further worsening of relations between the UK and Russia as he suggested that the nerve agent identified in Salisbury may have come from the UK Government’s nearby Porton Down defence laboratory.
Mr Johnson said Russia’s response to the incident was “not the response of a country that really believes itself to be innocent” as he detailed the UK’s belief that Moscow had been making chemical agents in recent years.
He told the Andrew Marr Show on BBC One: “I might just say in response to Mr Chizhov’s point about Russian stockpiles of chemical weapons, we actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination but has also been creating and stockpiling Novichok itself.”
He continued: “Listening to the Russian response, listening again to the response of the Russian ambassador to the EU, with his satirical suggestion that this was done by UK agents from Porton Down, this is not the response of a country that really believes itself to be innocent.
“This is not the response of a country that really wants to engage in getting to the bottom of the matter.”
Mr Chizhov had earlier suggested that Russia had never actually made the Novichok agent, telling the same programme: “No. Actually, Russia has stopped production of any chemical agents back in 1992.
“So you cannot even talk about any chemical agents produced by Russia. All that had been produced previously was produced by the Soviet Union.
“In 1992, the then president Boris Yeltsin signed a decree stopping all production and according to the international convention of prohibition of chemical weapons last year in 2017 Russia destroyed all its stockpiles.
“There is only one country today which hasn’t done so, which is still retaining its chemical stockpiles, and that is the United States of America.”
Salisbury spy attack timeline
He then appeared to suggest that the nerve agent may have come from Porton Down.
He said: “But when you have a nerve agent or whatever you check it against certain samples that you will retain at your laboratories and Porton Down as we now all know is the largest military facility in the United Kingdom, that has been dealing with chemical weapons research and it is actually only eight miles from Salisbury.”
Asked if he was actually suggesting that Porton Down may have been responsible for the nerve agent, he replied: “I don’t know. I don’t know.”
Theresa May told MPs in the House of Commons on Monday that Mr Skripal and his daughter were poisoned with Novichok “a military-grade nerve agent developed by Russia”.
Russian spy poisoning | Read more
The Prime Minister then said on Wednesday that there was “no alternative conclusion other than that the Russian state was culpable” for the poisoning as she expelled 23 Russian diplomats “identified as undeclared intelligence officers” in retaliation.
Russia responded on Sunday by expelling 23 UK diplomats.
Mr Johnson confirmed that experts from the Organisation for the Prohibition of Chemical Weapons will come to the UK on Monday to begin the process for the testing of samples of the nerve agent found in Salisbury.