Investigators find the highest concentration of the nerve agent Novichok on the Skripals’ front door.
Scientists at the UK's Porton Down defence laboratory have not been able to determine where the nerve agent used in the Salisbury spy attack was made, the boss of the facility has revealed.
Gary Aitkenhead, the chief executive of the Defence Science and Technology Laboratory (DSTL) at Porton Down, said that chemical weapons experts had "not verified the precise source" of the material but making the substance was "probably only within the capabilities of a state actor".
However, he said that "it is not our job" to determine precisely where the nerve agent, identified as belonging to the novichok family, was manufactured but he explained the work done at Porton Down formed part of the Government's wider intelligence picture.
A police officer at a cordon near the Maltings in Salisbury, England on Friday. Photo / AP
Aitkenhead also poured cold water on Kremlin suggestions that the material used to poison the former double agent Sergei Skripal and his daughter Yulia may have come from Porton Down which is located nearby to Salisbury.
Aitkenhead told Sky News: "We were able to identify it as novichok, to identify that it was a military-grade nerve agent.
"We have not verified the precise source, but we provided the scientific information to the government who have then used a number of other sources to piece together the conclusions that they have come to."
He added: "It is our job to provide the scientific evidence that identifies what the particular nerve agent is, we identified that it was from this family and that it is a military grade nerve agent, but it is not our job to then say where that actually was manufactured."
Theresa May, the Prime Minister, has blamed Russia for the poisonings and took action to expel 23 of Moscow's diplomats in the wake of the attack.
The Kremlin responded by expelling 23 British diplomats while many of the UK's allies then took their own action as they backed May's version of events.
Russia has denied wrongdoing and Sergei Lavrov, the foreign minister, recently accused the UK of "putting all decency aside" over its claims that Moscow is to blame.
Britain's Prime Minister Theresa May was quick to call out Russia being behind the attack. Photo / AP
He appeared to suggest that UK secret services may have been involved in the March 4 attack in Salisbury, which he said may have been "beneficial" to the Government to distract attention from Brexit.
Aitkenhead dismissed the claim and said: "There is no way that anything like that would ever have come from us or leave the four walls of our facilities.
"We deal with a number of very toxic substances as part of the work that we do.
"We have got the highest levels of security and controls. We are regularly audited by the OPCW (Organisation for the Prohibition of Chemical Weapons) to make sure we are operating within those controls and if there was any hint that anything that we have would be leaving our four walls then we wouldn't be allowed to operate."
Aitkenhead said it is possible to establish where the material came from "through a number of different input sources which the Government has access to".
"From our perspective, scientific evidence, it is only one of those sources and it requires a number of other things in order to verify that," he said.
He added: "At this stage with the work that we have done thus far we have been able to establish that it is novichok or from that family, we are continuing to work to help to provide additional information that might help us get closer to the question that you asked but we haven't yet been able to do that."
Aitkenhead said that Porton Down officials had been advising the medical team treating the Skripals to try to mitigate the effects of the nerve agent.
But he said "unfortunately this is an extremely toxic substance" and "there is not as far as we know any antidote that you can use to negate the effects of it".
Such a substance was "something that is probably only within the capabilities of a state actor" to produce, he said.
His intervention came as OPCW officials continued their investigation to verify the substance found in Salisbury.
Meanwhile a retired Russian general warned that the fallout from the Salisbury poisonings could lead to the "last war in the history of mankind".
Lieutenant-General Evgeny Buzhinsky said: "Please, when you say the world, you mean EU and United States and some other countries ... you see it's a cold war, it's worse than the Cold War because if the situation will develop in the way this (is) now, I'm afraid that it will end up in a very, very bad outcome."
Asked to spell out what this would mean, he said: "A real war, worse than a cold war is a real war, it will be the last war in the history of mankind."
A Downing Street spokesman said: "As the Prime Minister has made clear, the UK would much rather have in Russia a constructive partner ready to play by the rules.
"But this attack in Salisbury was part of a pattern of increasingly aggressive Russian behaviour, as well as a new and dangerous phase in Russian activity within the continent and beyond.
"As the Prime Minister has said, we must face the facts, and the challenge of Russia is one that will endure for years to come."
