Novichok is a military-grade nerve agent developed by Russian Federation from the 1970s onward, however the country's president Vladimir Putin has warned that it could be produced in up to 20 countries.
Russian Federation yesterday accused the United Kingdom of trying to "block Yulia from the outside world" after a statement from the 33-year-old declined help from its embassy.
Russian intelligence agents hacked Yulia Skripal's emails for at least five years before the Salisbury poisonings, a bombshell Government dossier has revealed.
In the statement published on Wednesday, she said her father remained seriously ill and that she was still suffering from the effects of nerve agent used against them.
Sir Mark also identified the key institute for developing Novichok in the former Soviet Union as a branch of the State Institute for Organic Chemistry and Technology near Volgograd. Russia's ambassador to Britain Aleksandr Yakovenko expressed surprise and asked two questions: what the reasons for spying on Skripal in London after his release in Moscow were and why British special services had never complained Skripal was under surveillance.
In his letter, Mr Sedwill backed his Mr Johnsons claims, adding that Russian Federation had "produced and stockpiled small quantities of novichoks" under the training programme on chemical weapons in the 2000s.
"It is highly likely that Novichoks were developed to prevent detection by the West and to circumvent worldwide weapons controls", he said.
Police investigating the Salisbury poisoning said the highest concentration of the Novichok nerve agent had been found on Sergei Skripal's front door. Moscow rejected all of the United Kingdom's accusations, saying that a program aimed at developing such a substance had existed neither in the Soviet Union nor in Russian Federation.
Sergei Skripal, a former colonel in Russian military intelligence who betrayed dozens of agents to Britain's MI6 foreign spy service, and his daughter were found unconscious on a bench in the English cathedral city of Salisbury on March 4.
Britain said the report's characterization of the substance as highly purified supported its stance that the chemical could have been produced only by a state laboratory, although Moscow refuses to provide samples against which it could be matched.
"There is no plausible alternative explanation", he added. 'So far, we doubt it much.
He went on: "We didn't produce and store Novichok, so this is the fact of life and all these allegations that we produce something have nothing to do with the reality".
In the statement, Skripal said no one but they themselves could speak for her and her father.
The police officer who was severely affected by the nerve agent, DS Nick Bailey, was allowed to leave hospital three weeks ago.