His daughter, who lives in Moscow, was visiting him when the two were poisoned in an attack that has triggered an worldwide diplomatic crisis between Russia and the West. Sedwill's letter to NATO Secretary General Jens Stoltenberg alleged that Russia had "the technical means, operational experience and motive for the attack on the Skripals and that it is highly likely that the Russian state was responsible".
The national security adviser said that President Putin "was closely involved in the Russian chemical weapons..."
The news which has been hailed as a significant milestone, comes just over a month after the pair were found slumped over on a park bench in the English city, after they were poisoned by a deadly nerve agent.
The testimony of the Skripals will be crucial in establishing the credibility of the British government's claim that it was "highly likely" that the Russian state had targeted them with the nerve agent.
The worldwide watchdog agency that monitors the use of chemical weapons said on Thursday that its independent investigators had confirmed Britain's assertions that the chemical used to poison former Russian double agent Sergei Skripal and his daughter was a military-grade nerve agent known as Novichok.
According to the embassy's maycommentary, "the case against Russian Federation is based on three elements: the identification of the chemical agent, far-fetched speculations and conclusions regarding the "operational experience" and "motive", as well as unverifiable 'intelligence'". The key institute responsible for this work was a branch of the State Institute for Organic Chemistry and Technology at Shikhany defence laboratory, near Volgograd in south-west Russian Federation. British Prime Minister Theresa May has said it is highly likely that Moscow was behind the attack.
"We didn't produce Novichok, we never have - that's the official position", he said.
The experts took samples from several locations as well as biomedical samples from the Skripals and police officer Nick Bailey, who was also exposed to the nerve agent. Former KGB bodyguards identified as suspects in the murder denied any involvement.
"Russia's chemical weapons programme continued after the collapse of the Soviet Union". In her statement, she said that she has been made aware of the Russian embassy's attempts to contact her but she did not wish to avail of their services for the moment.
"The Russian state has previously produced Novichoks and would still be capable of doing so".
Russian Federation has charged that British officials are keeping Skripal's daughter in isolation. Ambassador Alexander Yakovenko said the embassy would be publishing its own 33-page report about the incident.
In a statement issued on Wednesday via police Yulia said she was "seeking to come to terms with my prospects, while also recovering from this attack on me".