Defence lab unable to definitively say where nerve agent that poisoned Sergei Skripal and his daughter came from

British scientists at the Porton Down defence research laboratory have not established that the nerve agent used to poison Sergei and Yulia Skripal was constructed in Russia, it has emerged.

Gary Aitkenhead, the chief executive of the government's Defence Science and Technology Laboratory( DSTL ), said the poison had been identified as a military-grade novichok nerve agent, which could probably be deployed merely by a nation state.

Aitkenhead said the government had reached its conclusion that Russia was responsible for the Salisbury attack by combining the laboratory's scientific findings with datum from other sources.

The UK government moved quickly to make it clear that the prime minister, Theresa May, had always been clear the assessment from Porton Down was ” merely one part of the intelligence picture “. The remarks came hours before an extraordinary meeting in The Hague of the executive council of the Organisation for the Prohibition of Chemical Weapons( OPCW ), called by Russia.

Speaking to Sky News, Aitkenhead said it was not possible for scientists alone to say precisely where the novichok had been created.

He said:” It's a military-grade nerve agent, which requires highly sophisticated methods in order to create- something that's probably only within the capabilities of a state actor .”

He denied Russian claims that the substance could have come from Porton Down, which is eight miles from Salisbury, saying:” There's no way that anything like that would ever have come from us or leave the four walls of our facilities .”

Aitkenhead said:” We were able to identify it as novichok, to identify it was a military-grade nerve agent. We have not confirmed the precise source, but we have provided the scientific information to the government, “whos had” then utilized a number of other sources to piece together the conclusions that they have come to .”

He said the location of fabricate could be established through” a number of different input sources which the government has access to”, adding:” Scientific evidence is only one of those sources .”

Aitkenhead said Porton Down was continuing to work on the substance to try to provide additional information that might help.

He also said there was no known antidote to novichok but said Porton Down had advised Salisbury district hospital on how to treat the Skripals.

Seizing on Aitkenhead's remarks, Vladimir Putin's spokesman Dmitry Peskov said Britain will have to apologise to Russia for its” mad accusations” that “have no foundation whatsoever.”

The Russian embassy in London said the UK's claims that Moscow was behind the attack was a ” bluff” and added:” This has been confirmed by the head of the secret lab. This only proves that all political declarations on the Russian origin of the crime are nothing but hypothesis not stemming from objective facts or the course of the investigation .”

A UK government spokesman played down the signficance of Aitkenhead's statements. He said:” We have been clear from the very beginning that our world-leading experts at Porton Down identified the substance used in Salisbury as a novichok.

” This is only one part of the intelligence picture. As the prime minister has set out in a number of statements to the Commons since 12 March, 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.

” It is our assessment that Russia was responsible for this brazen and reckless act and, as the world community concurs, it is not possible to other plausible explain .”

However, two weeks ago Boris Johnson was asked by an interviewer on Deutsche Walle, Germany's public international broadcaster, how the UK had been able to find out the novichok were derived from Russia so quickly.

He replied:” When I look at the evidence, the people from Porton Down, the laboratory, they were absolutely categorical. I asked the guy myself, I said:' Are you sure ?' And he said:' There's no doubt .' So we have very little alternative but to take the action that we have taken .”

Looking ahead to Wednesday's OPCW meeting, a Foreign Office spokesman said Russia had called it to try to undermine the work of the organisation. The spokesman said:” This Russian initiative is yet again another diversionary tactic, intended to undermine the work of the OPCW in reaching a conclusion .”

The Russian ambassador to Ireland, Yury Filatov, was the latest to join the criticism from Russia over the UK's handing of the aftermath of the attack.

He said Russia wanted Britain to” provide every possible component of evidence” it had, adding:” We certainly reject any notion or claim of Russian involvement in the Salisbury incident. We will not tolerate this kind of irresponsible and basically indecent behaviour on the part of the British government. They will have to answer for that .”

Russia's deputy foreign minister, Alexander Grushko, called the attack a” provocation arranged by Britain” to justify high military spending because” they need a major foe “.

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