https://sputniknews.com/world/201803201062711423-novichok-nerve-agent-skripal/

London is not providing Moscow with a sample of the substance that poisoned former GRU Colonel Sergei Skripal, because the Russian experts are able to quickly determine that it was not manufactured in Russia, Leonid Rink, one of the developers of the Novichok chemical weapons system said in an interview with Sputnik.

"Why do you think the British refuse to give a [nerve agent] sample to Moscow? Because no matter how hard the specialists try, the manufacturing technology always differs a little. It's a kind of a 'handwriting sample.' It will immediately become clear that this is not a Russian technology," Rink said.

Rink added that the sample from Salisbury is like a "fingerprint" for a forensic expert.
"It could be easily determined that it [the poison] was not 'cooked' in Russia," he stressed.
According to the scientist, British chemical weapons experts had access to Novichok technology and could have used it to poison Skripal and his daughter.
"It [the Novichok-type technology] is commonly available for professionals…Any pharmaceutical corporation, any chemical corporation is capable of manufacturing it in their laboratories," Rink said.
"It is absolutely certain that there are such specialists in the UK. I believe they could have applied the substance on Skripal or his daughter's belongings. Or on some objects in the cemetery. Naturally, there should have known that Skripal would visit the cemetery. It could have easily been done by the British themselves," he concluded.

Former Russian intelligence officer Skripal and his daughter were found unconscious on a bench near a shopping center in the UK city of Salisbury on March 4. Subsequent investigation of the case revealed that the two were poisoned with a military-grade nerve agent believed to be developed in secrecy by the former Soviet Union.
As the victims remain at the hospital in critical conditions, the highly publicized poisoning incident has triggered a massive diplomatic fallout between London and Moscow; UK authorities have accused Russia of being behind the attack and expelled 23 Russian diplomats, vowing additional punitive measures. Russian officials called such allegations groundless and responded by declaring 23 employees of the UK Embassy in Moscow personae non gratae.
Russia has demanded access to the case'a materials, including the nerve gas, allegedly used to poison Skripal, however, London has refused to do so according to Foreign Minister Sergei Lavrov.
UK Foreign Secretary Boris Johnson has claimed that there is evidence that Russia has been stockpiling the nerve gas, while Russian Foreign Ministry spokeswoman Maria Zakharova has said that the deadly substance may have originated from the Czech Republic, Slovakia, Sweden, the United Kingdom, or the United States.