Britain has evidence that Russia has been stockpiling and creating a deadly nerve agent used in the poisoning of a former Russian spy for the last 10 years, the foreign secretary Boris Johnson has said.
Speaking on The Andrew Marr Show on Sunday, he said: "We actually have evidence within the last 10 years, Russia has not only been investigating the delivery of nerve agents for the purposes of assassinations but has also been creating and stockpiling Novichok."
A statement from the Foreign Office released after Johnson's television appearance said that if the evidence was correct, it amounted to "a violation of the Chemical Weapons Convention".
Speaking on Monday, Johnson went on to say Russian denials of involvement in the attack were growing "increasingly absurd".
However, shortly after winning a new term in a presidential election, Russian president Vladimir Putin denied Moscow's involvement.
“I think any sensible person would understand that it would be rubbish, drivel, nonsense, for Russia to embark on such an escapade on the eve of a presidential election," he said.
However, Describing the attack on Sergei Skripal and his daughter Yulia on the Marr show, Johnson said: "To the best of our knowledge this is a Russian-made nerve agent that falls within the category of Novichok, made only by Russia."
He went on: "We gave the Russians every opportunity to come up with an alternative hypothesis ... and they haven’t. Their response has been a sort of mixture of smug sarcasm and denial, obfuscation and delay.”
The British research lab at Porton Down in Wiltshire identified the substance used on the Skripals as part of a group of military-grade nerve agents, created by Russia and known as Novichok.
Earlier, Russia's ambassador to the EU, Vladimir Chizhov, suggested that the British research laboratory itself could be the source of the nerve agent.
He told Andrew Marr: "When you have a nerve agent or whatever, you check it against certain samples that you retain in 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's actually only eight miles from Salisbury."
A spokesperson for the Foreign Office said: "It's just another futile attempt from the Russian state to divert the story away from the facts – that Russia has acted in flagrant breach of its international obligations," while Johnson said it was indicative that Russia was "not a country that wants to engage in getting to the bottom of the matter."
Johnson announced that tomorrow technical experts from the Organisation for the Prohibition of Chemical Weapons will come from the Hague to the UK. He said: "We will share the samples with them, they will then be tested by the most reputable international laboratories."
Johnson had harsh words for Russia, adding: "People have all now experienced, whether it's in America, Germany, France – say nothing of the Baltic countries, the Balkans, and Poland – they've all experienced Russian meddling, malign, disruptive Russian behaviour over the last few years. They can see a country that's going in the wrong direction."
He said: "One of the things that has struck me is the difference between their reaction this time, and their reaction to the death of Alexander Litvinenko – then in 2006 there was much more hesitation. ... Now you have people such as the US ambassador to the UN ... pointing the finger squarely at Russia. That indicates the change in people's attitudes to Russia."
"I think it's obvious they do care. They look at us and think, This is the country that time and again has called Russia out."
However, he went on: "It's important we don't allow a miasma of suspicion about all Russians in London and indeed all rich Russians in London [to develop]."
John McDonnell, the shadow chancellor, appeared on Peston on Sunday and took a harder stance than the Labour leader Jeremy Corbyn, saying Theresa May was right to directly blame Vladimir Putin.
“I agree with the prime minister,” McDonnell said. “I agree completely with the prime minister. What she’s said is that Russia is culpable, either by direct commission – Putin’s ordered this – or they’ve lost control of their supplies.”
McDonnell added: “He is responsible, whichever way you look at it. He is responsible, and all the evidence points to him.”
Labour will support tough action against Russia, including economic sanctions, the shadow chancellor said.
The foreign secretary described the Kremlin’s countermeasures after the UK pledged to expel 23 Russian diplomats – expelling the same number of British diplomats and closing the British consulate in St Petersburg and the British Council – would only impact on Russians.
Writing in the Sun on Sunday, Johnson said: "These futile measures will only punish ordinary Russians by depriving them of harmless opportunities to learn English and apply for UK visas."
However, he suffered an awkward moment during the interview after being grilled about the wife of a Putin minister paying £160,000 for a game of tennis with him. "If there's evidence of gross corruption about the way that gentleman obtained his wealth it's possible for our authorities to deprive him," Johnson answered.
After being asked again for an answer about whether the game took place, he confirmed: "it did".
Shortly after Johnson's interview finished, the Russian Embassy in the UK responded with a picture of the TV detective Hercule Poirot, provoking a furious response from some Labour and Tory MPs.
This post has been updated to more accurately quote Boris Johnson's appearance on The Andrew Marr Show.