Up to 100 grams of liquid nerve agent were used in the attack on former Russian spy Sergei Skripal and his daughter Yulia, the head of the Organisation for the Prohibition of Chemical Weapons (OPCW) has said.
Ahmet Uzumcu told the New York Times the amount of Novichok used - around half a cup of liquid - suggests it was created for use as a weapon rather than for research purposes.
Mr Skripal, 66, and his 33-year-old daughter Yulia were left fighting for their lives in hospital after being found unconscious on a park bench in Salisbury on March 4.
The inquiry into the nerve agent attack in the Wiltshire city has involved 250 detectives who have gone through more than 5,000 hours of CCTV and interviewed more than 500 witnesses.
What is Novichok
He said: "For research activities or protection you would need, for instance, five to 10 grams or so, but even in Salisbury it looks like they may have used more than that, without knowing the exact quantity, I am told it may be 50, 100 grams or so, which goes beyond research activities for protection.
"It's not affected by weather conditions. That explains, actually, that they were able to identify it after a considerable time lapse."
He added the samples collected suggested the nerve agent was of "high purity".
Moscow has denied accusations it was responsible for the poisoning of the Skripals but the incident plunged diplomatic relations between Russia and the West into the deep freeze.
The Russian ambassador to the UK Alexander Yakovenko previously suggested that Sergei and Yulia Skripal may have been injected by British authorities with nerve agent produced at Porton Down.
Timeline Sergei Skripal How events have unfolded
However the UK has previously stated its conviction that only Russia had the means and motive to target the former spy.
Karen Pierce, the UK's representative to the United Nations, told a meeting last month there was "no plausible alternative explanation than Russian State responsibility for what happened in Salisbury", suggesting Russia had the ability, operation experience and motive to carry out the attack.
She said: "Russia has a proven record of conducting state-sponsored assassinations including on the territory of the United Kingdom.
"The independent inquiry into the death of Alexander Litvinenko concluded in January 2016 that he was deliberately poisoned with polonium; that the FSB had directed the operation; and that President Putin probably approved it."
On the technical means of creating Novichok, she said: "No terrorist group or non-state actor would be able to produce this agent in the purity described by the OPCW testing and this is something Russia has acknowledged.
"The Russian State has previously produced Novichoks and would still be capable of doing so today."