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The Foreign Office has been forced to delete a tweet claiming Porton Down confirmed the nerve agent used in the Salisbury attack was "produced in Russia".

Officials scrambled to remove the tweet from March 22 after the UK's chemical weapons lab said it confirmed no such thing - and was never supposed to.

It comes as Foreign Secretary Boris Johnson stands accused of "misleading the public" after he also suggested Porton Down had traced the nerve agent used on Sergei Skripal to Russia.

The tweet - which supposedly quoted Britain's ambassador to Moscow - claimed analysis by Porton Down "made clear" the nerve agent used to poison ex-spy Sergei Skripal was "produced in Russia".

But Porton Down says it did not provide that confirmation. Instead its analysis was combined with other intelligence to point the finger at Russia, officials say.

(Image: PA)

The Foreign Office today confirmed it had deleted the tweet, saying it was "truncated" and inaccurately reported the words of Laurie Bristow.

A transcript by the Foreign Office claims Mr Bristow actually said the agent was "of the Novichok series; a nerve agent produced in Russia." No video is available of the moment he said it.

The slip-up was an instant propaganda gift to President Vladimir Putin - who has already seized on Porton Down's comments as proof Britain had rushed to judge the Kremlin too soon.

The Russian Embassy tweeted: "Why would the Foreign Office delete this tweet from 22 March?"

Spot the difference: What a UK Foreign Office tweet and transcript said about Novichok Foreign Office Tweet about UK Ambassador to Moscow Laurie Bristow speech on 22 March: "Analysis by world-leading experts at the Defence Science and Technology Laboratory at Porton Down made clear that this was a military-grade Novichok nerve agent produced in Russia." Transcript of speech on Foreign Office website: "Analysts at Porton Down, the Defence Science and Technology Laboratory in the UK, established and made clear that this was a military-grade chemical weapon. One of the Novichok series; a nerve agent as I said produced in Russia."

The row kicked off yesterday when the chief executive of Porton Down said his lab had not traced the deadly Novichok to Russia.

Gary Aitkenhead's comments, branded "clearly unhelpful" by a senior minister, provoked a scramble in Downing Street.

Last night a government spokesman stressed "we have been clear from the very beginning" that Porton Down was "only one part of the intelligence picture".

Porton Down last night added: "It is not and has never been our responsibility to confirm the source of the agent".

Yet Mr Aitkenhead's comments muddied the waters - and spelt a PR disaster for Foreign Secretary Boris Johnson.

Last month Mr Johnson personally suggested the military lab had confirmed the poison's source.

Asked how he knew Russia was the source of the nerve agent, the Foreign Secretary told a German newspaper on March 20: "When I look at the evidence, I mean the people from Porton Down, the laboratory … [Asked if they have samples]. They do.And they were absolutely categorical and I asked the guy myself, I said, 'Are you sure?' And he said there's no doubt.”

Labour leader Jeremy Corbyn today accused Mr Johnson of "exaggeration", said he had "egg on his face" and added: "Boris Johnson has serious questions to answer.

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"He claimed on German TV that this was a Russian-produced nerve agent .

"Porton Down then examined it and said all they could identify is as was Novichok. They couldn’t say where it came from.

"The Foreign Office then issued a tweet in support of what the Foreign Secretary said, then removed that yesterday after Porton Down said they couldn’t identify the source of it.

"So Boris Johnson seems to have completely exceeded the information that he’d been given and told the world in categorical terms what he believed had happened.

"And it’s not backed up by the evidence he claimed to have got from Porton Down in the first place."

Shadow Home Secretary Diane Abbott added: "It seems Boris Johnson misled the public when he claimed that Porton Down officials confirmed to him that Russia was the source of the nerve agent used in the Salisbury attack.

(Image: REUTERS)

"Those officials have made it clear they cannot identify its source, and are not able to definitively say it came from Russia or elsewhere.

"Boris Johnson is supposed to represent Britain on the world stage, but time and again he has shown he is unable to do so responsibly.”

Russia took the Salisbury nerve agent attack row to The Hague today after Vladimir Putin blasted Britain in an escalating global spat over who is responsible.

President Putin seized on the comment by Porton Down as the Kremlin called the extraordinary meeting of the Organisation for the Prohibition of Chemical Weapons (OPCW).

Mr Putin referenced the Porton Down comments and declared: "The speed at which the anti-Russian campaign has been launched causes bewilderment."

(Image: AFP)

But the UK's permanent representative to the OPCW accused Russia of showing "disdain" for its independence.

John Foggo told an extraordinary meeting of the body's executive council in The Hague: "Russia's statements demonstrate a wilful ignorance of the Convention's provisions and, worse than that, a disdain for the independence and competence of the Technical Secretariat."

Commenting on Boris Johnson's interview, a Government spokesman said: "The Foreign Secretary was making clear that Porton Down were sure it was a Novichok - a point they have reinforced.

"He goes on in the same interview to make clear why based on that information, additional intelligence and the lack of alternative explanation from the Russians, we have reached the conclusion we have.

"What the Foreign Secretary said then, and what Porton Down have said recently, is fully consistent with what we have said throughout. It is Russia that is putting forward multiple versions of events and obfuscating the truth."

(Image: AFP)

Commenting on the deleted tweet, a Foreign Office spokesman said: "An HMA Moscow briefing on 22 March was tweeted in real time by @UKinRussia and amplified by @foreignoffice, to explain what happened in Salisbury to as wide an audience as possible.

"One of the tweets was truncated and did not accurately report our Ambassador’s words. We have removed this tweet.

"None of this changes the fact that 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.

"No other country has a combination of the capability, the intent, and the motive to carry out such an act."

Security minister Ben Wallace said the Government took time to assess the evidence and intelligence before accusing Russia.

He told BBC Radio 4's The World At One: "Scientists are scientists. I, as well as national security, have organised crime, terrorism under my portfolio, and when we work with forensic scientists, the scientists tell us what something is - they tell me a gun and a type of gun was used - but the attribution of who used it, exactly how it was used is a matter for the broader investigation.

"That includes intelligence, detectives if it's a police investigation, and the scientists as well, and that's perfectly understandable."

Pressed further, Mr Wallace said: "Porton Down will be able to tell you there are very, very, very few people in the world who, first of all, did design Novichok - and that was the Russians - and who have developed and stockpiled it.

"In fact the task of that is reduced to one."