PORTON Down scientists have not been able to establish where the novichok nerve agent used to poison Sergei and Yulia Skripal was made, it has emerged.

Gary Aitkenhead, the chief executive of the Defence Science and Technology Laboratory (DSTL) at Porton Down, Wiltshire, said it had not proved it was created in Russia.

Mr Aitkenhead has also dismissed Russian claims that the nerve agent used in Salisbury might have come from the defence laboratory, and said that its deployment was "probably only within the capability of a state actor".

Mr Aitkenhead told Sky News: "We, in terms of our role, were able to identify it as Novichok, to identify it was a military grade nerve agent.

"We have not verified the precise source but we provided the scientific information to the government who have then used a number of other sources to piece together the conclusions that they have come to.

"It's our job to provide the scientific evidence that identifies what the particular nerve agent is.

"We identified that it was from this family and that it's a military grade nerve agent but it's not our job to then say where that actually was manufactured.”

Aitkenhead would not comment on whether the laboratory had developed or kept stocks of novichok, but dismissed the suggestion from Russia that the agent used to poison the Skripals could have come from Porton Down.

“There is no way anything like that could have come from us or left the four walls of our facility,” said Aitkenhead.