'You expel diplomats, we expel diplomats, you further expel, what's the next step?
The defence research facility, which identified the substance in Salisbury as Novichok, said it was likely to have been deployed by a "state actor".
Testing had shown that it was military grade nerve agent but it could not be shown to have come from Russian Federation, said Gary Aitkenhead, the chief executive of the Defence Science and Technology Laboratory at Porton Down.
Gary Aitkenhead, chief executive at Porton Down, the UK Ministry of Defence's science lab, told Sky News on Tuesday that investigators have identified the poison to be military-grade Novichok, which was designed in Russian Federation during the Cold War, but "have not verified the precise source" of it.
The admission is likely to be seized on by Russian Federation which has suggested that the nerve agent could have come from other nations, or from Porton Down, which is eight miles from Salisbury, the scene of the attack. Russia's European Union ambassador Vladimir Chizhov noted in an interview with the BBC last month that the British research lab is only eight miles (11 km) from Salisbury, insinuating that may have been the source.
The British authorities are preparing to grant her a visa so that she can become the first family member to meet Yulia, and also see her uncle Sergei, who remains in a coma.
In a letter, Russia's ambassador to the OPCW, Alexander Shulgin, asked for the meeting to discuss Britain's allegations "in a confidential sitting". The United Kingdom was requested to reduce the number of its diplomatic staff in Russia so that it would match the number of Russian diplomats in Great Britain.
OPCW experts have taken samples from Salisbury to try to verify the nerve agent used and its origin.
In comments reported by Russian news agencies, Mr Grushko said the attempted murders could have been "arranged by Britain" because "they need a major enemy".
A former Russian general has warned world is on the brink of "the last war in the history of mankind" over the poisoning of a spy.
Speaking on the Today programme, Mr Buzhinsky warned how the reaction from Russian Federation over the expelled diplomats could lead to the "last war in the history of mankind", ramping up World War 3 fears.
Former Lieutenant-General Evgeny Buzhinskiy.
"You say Russian Federation should change its behaviour, it's not the kind of talk or compromise we need. Actually but you are cornering Russian Federation, and to corner bring Russian Federation is a very bad thing".
London's reluctance to share information on the poisoning of former double agent Sergei Skripal has led Moscow to strongly suspect that it was the actual perpetrator of the crime, the Russian ambassador to Britain said.