He also said Russia had a clear motive for attacking Skripal, a former Russian military intelligence officer who had been imprisoned in Russia for spying for Britain only to be set free in a spy swap.
Russian intelligence agencies had been spying on Sergei and Yulia Skripal for at least five years before they were poisoned with a nerve agent, Britain's National Security Adviser Mark Sedwill said on April 13. Britain has blamed Russian Federation for the attempted murder - a charge that Moscow fiercely denies.
Moscow has suggested Britain carried out the attack to stoke anti-Russian hysteria, but Britain asked the Organisation for the Prohibition of Chemical Weapons (OPCW) to check samples from Salisbury.
Mark Sedwill also said in a letter to NATO Secretary General Jens Stoltenberg that Russian Federation had previously tested whether door handles could be used to deliver nerve agents.
Turning to how exactly nerve agents are used by Russia, Sedwill said: "During the 2000s, Russia commenced a programme to test means of delivering chemical warfare agents and to train personnel from special units in the use of these weapons".
The chemical weapon used in Salisbury was of "high purity", the watchdog said.
It goes on to say that "during the 2000s", Russian Federation created a special unit to develop chemical weapons for use as tools in state-sponsored attacks and to "train personnel from special units in the use of these weapons".
Ms Skripal, who was released from hospital this week, said in a statement she was still suffering effects of the poisoning and her father remained seriously ill.
In an account based in part on declassified United Kingdom intelligence, Sir Mark also said the Russians had developed a programme in the 2000s to train personnel from "special units" in the use of chemical warfare agents.
British Foreign Secretary Boris Johnson hailed the findings, and said "only Russia" could have been behind the attack.
In it, Sedwill alleged Russia's GRU military intelligence service had its cyber experts break into Yulia's email in 2013.
A program set up in Russian Federation in the 2000s trained personnel from special units in the use of chemical warfare agents, he said, including investigating how nerve agents could be administered through door handles.
Speaking on Friday, Sergey Lavrov, Russia's foreign minister, said the OPCW report offers nothing to support Britain's claims that Russia was behind the attack. "Within the last decade, Russian Federation has produced and stockpiled small quantities of Novichoks under the same program".
"Mr. Skripal and his daughter were poisoned with a military-grade nerve agent of a type developed by Russian Federation", specifically from the Novichok group, British Prime Minister Theresa May said after the incident, based on an assessment by British experts.
He then claimed Russian Federation saw at least some of its defectors as legitimate targets for assassination, suggesting Skripal could be among them.