The head of the Porton Down military research facility has said his scientists have not verified that the nerve agent used in Salisbury came from Russia.
Gary Aitkenhead, the chief executive of the Government’s Defence Science and Technology Laboratory, said the poison had been identified as a military-grade Novichok nerve agent which could probably be deployed only by a nation-state.
But he told Sky News it was not Porton Down’s role to work out its origin and said the Government relied on “a number of different input sources” in coming to its assessment that it was highly likely to be from Russia.
Mr Aitkenhead flatly denied Russian claims the substance could have come from Porton Down itself.
A Government spokesman said that the authorities had always been clear that the Porton Down assessment was “only one part of the intelligence picture”.
“As the Prime Minister has set out in a number of statements to the Commons since March 12, this includes our knowledge that within the last decade, Russia has investigated ways of delivering nerve agents probably for assassination and as part of this programme has produced and stockpiled small quantities of Novichoks; Russia’s record of conducting state-sponsored assassinations; and our assessment that Russia views former intelligence officers as targets,” said the spokesman.
“It is our assessment that Russia was responsible for this brazen and reckless act and, as the international community agrees, there is no other plausible explanation.”
Mr Aitkenhead’s comments come a day ahead of an extraordinary meeting in The Hague of the executive council of the Organisation for the Prohibition of Chemical Weapons to discuss the Salisbury attack.
The meeting on April 4 - to be held behind closed doors - was called by Russia to “address the situation around allegations of non-compliance” with the chemical weapons convention made by the UK against Moscow.
But the Foreign Office dismissed it as a “diversionary tactic” by Russia, “intended to undermine the work of the OPCW in reaching a conclusion”.
Russia has denied responsibility for the March 4 attack on former spy Sergei Skripal and his daughter Yulia, with foreign minister Sergey Lavrov even suggesting on Monday that it might have been carried out by the UK as a means of distracting voters from its difficulties with Brexit.
Mr Lavrov said relations between Russia and the West were worse than during the Cold War, accusing the UK and US of “putting all decency aside” in their dealings with Moscow.
Porton Down’s identification of the substance used in the attack on the Skripals as Novichok was a key plank in the evidence presented by the UK in Theresa May’s successful bid to recruit international support in the dispute with Moscow, resulting in the expulsion of more than 100 Russian diplomats from over 20 countries.
Asked about his scientists’ findings, Mr Aitkenhead told Sky: “We in terms of our role were able to identify it as Novichok, to identify it was a military-grade nerve agent.
“We have not verified the precise source, but we have 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.”
The location of manufacture “can be established through a number of different input sources which the Government has access to”, he said, adding: “From our perspective, scientific evidence is only one of those sources, and it requires a number of other things to verify that.
“It’s a military grade nerve agent which requires extremely sophisticated methods in order to create - something that’s probably only within the capabilities of a state actor.”
Rejecting Russian claims the substance could have come from Porton Down, Mr Aitkenhead said: “There’s no way that anything like that would ever have come from us or leave the four walls of our facilities.
“We’ve got the highest levels of security and controls. We are regularly audited by the OPCW to make sure we are operating within those controls. If there was any hint that anything that we have would be leaving our four walls, then we wouldn’t be allowed to operate.”
Meanwhile, retired Russian Lieutenant-General Evgeny Buzhinsky warned that relations between Russia and the West could become “worse” than the Cold War and “end up in a very, very bad outcome” following the nerve agent attack.
Asked to spell out what this would mean, he told BBC Radio 4’s Today programme: “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.”