Russia has suggested that the nerve agent used to poison former spy Sergei Skripal and his daughter, could have come from a UK-based high-security facility. But the chief executive of Britain's Porton Down defence laboratory has dismissed the claim.

GARY AITKENHEAD CHIEF EXECUTIVE OF PORTON DOWN "We, in terms of our role were able to identify it as Novichok, to identify that it was a military grade nerve agent. We have not verified the precise source. 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 military grade nerve agent but it's not our job to then see where that actually was manufactured."