Scientists from Porton Down have not been able to establish where the novichok nerve agent used to poison Sergei and Yulia Skripal was made.
Gary Aitkenhead, chief executive of the Defence Science and Technology Laboratory (DSTL) at Porton Down, told Sky News they were not yet able to prove it was made in Russia.
He said: “We were able to identify it as novichok, to identify that it was military-grade nerve agent.
Stay informed:
The Emergency Election Sale is now live! Get 30% to 60% off our most popular products today!