Russia has requested the United Nations Security Council meet tomorrow to discuss British accusations that it used a nerve agent to attack a former Russian spy in England last month.

Russian UN Ambassador Vassily Nebenzia said the meeting would be convened on the basis of a 13 March letter sent to the UN Security Council by British Prime Minister Theresa May, which said Russia was "highly likely" to be responsible for the attack.

The 15-member council first met on 14 March, at the request of Britain, to discuss the attack in Salisbury.

Britain has criticised as "perverse" Russia's call for a joint investigation into the poisoning of Sergei Skripal and his daughter Yulia.

"Russia's proposal for a joint, UK/Russian investigation into the Salisbury incident is perverse. It is a diversionary tactic," the British delegation to the Organisation for the Prohibition of Chemical Weapons (OPCW) said in a tweet.

Russia was seeking to "evade the questions the Russian authorities must answer," it added.

The British delegation to the OPCW, led by top chemical weapons expert John Foggo, was attending a meeting of the body's governing executive council in The Hague.

Five things to know about the OPCW

Russia's ambassador to the Netherlands and deputy minister for industry and trade Georgy Kalamanov also attended, along with Mr Foggo.

The Russians hit back on Twitter, saying they had won the backing from 14 countries for their joint statement to the council.

"We consider this is necessary to ensure that this problem is solved within the (international) legal framework," the Russian embassy to the Netherlands said in a Tweet.

It added that its statement to the council was "supported by solid facts by experts in this field" and insisted that Russia was ready "to cooperate both with and within OPCW."

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Earlier, Russia's foreign intelligence agency chief Sergei Naryshkin has said that the poisoning of the Skripals was an act of provocation by US and British intelligence services.

"Even in the Skripal case, a grotesque provocation crudely concocted by US and British security services, some European governments are not following London and Washington blindly but are instead choosing to carefully make sense of what happened," Mr Naryshkin said.

He also said that Washington's actions towards Russia mean it is possible to start speaking of a return to the Cold War era.

"Washington has become fixated with the fight against a non-existent, so-called Russian threat. This has reached such proportions and acquired such absurd characteristics that it's possible to speak of a return to the dark times of the Cold War," the spy chief said, speaking at a security conference in Moscow.

President Vladimir Putin has said he hopes today’s closed-door meeting of the executive council of the OPCW at The Hague will draw a line under any suggestion of Russian involvement in the Salisbury attack.

A team from the OPCW has been in Salisbury in recent weeks collecting and assessing evidence as part of an investigation into the attack.

The organisation was also granted permission to take blood samples from both Sergei and Yulia Skripal to help in the inquiry.

Mr Skripal remains in a critical but stable condition in hospital, while Yulia is said to be improving.

The EU has said Russia must cooperate with the OPCW.

"It is imperative that the Russian Federation responds to the British government's legitimate questions, begins to co-operate with the OPCW Secretariat, and provides full and complete disclosure to the OPCW", it said in statement read out at the meeting.

The OPCW meeting comes a day after the head of the UK’s military research facility at Porton Down said his scientists have not verified that the nerve agent used in Salisbury came from Russia.

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

However, he told Sky News it was not Porton Down's role to work out where the agent came from and suggested the government's conclusion that it was highly likely to have come from Russia was based on "a number of other sources".

President Putin, citing Mr Aitkenhead, called for a thorough investigation into the poisoning during a visit to Turkey, where he said "the speed at which the anti-Russian campaign has been launched causes bewilderment".

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 bid to recruit international support in the dispute with Russia.

It has resulted in the expulsion of more than 100 Russian diplomats from more than 20 countries, including Ireland.