The Skripals are believed to have been poisoned with the nerve agent Novichok, and the fallout from the attack on them has resulted in the expulsion of Russian diplomats from the United Kingdom and its allies, since the Government concluded that it was "highly likely" that the blame lay with Moscow (News, 16 March, 23 March).
The Organisation for the Prohibition of Chemical Weapons (OPCW) did not identify who made it, but the foreign secretary said only Russian Federation had the "means, motive and record".
Sedwill also said that Russian Federation has tested means of delivering chemical agents "including by application to door handles", pointing out that the highest concentration of the chemical found after the attack was on Skripal's front door handle.
The UK's defence laboratory at Porton Down had established the highest concentrations of the poison were found on the handle of Sergei Skripal's front door, the letter said. In the 2000s, Sedwill said Russian Federation had trained military personnel in using these weapons, including on door handles, and Russian Federation "has a proven record of conducting state-sponsored assassination".
Sedwill also said in the letter, which was published by the government, that it was "highly likely that the Russian intelligence services view at least some of its defectors as legitimate targets for assassination". 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.
U.K. Prime Minister Theresa May rallied allies in the U.S., Europe, Australia and Canada to conduct coordinated expulsions of more than 150 Russian diplomats last month after she told parliament it was "highly likely" that Russia was responsible. So far, we doubt it much.
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.
The letter revealed that Russia's chemical weapons programme continued after the collapse of the Soviet Union.
He repeated previous statements that the Russian state has previously produced Novichoks and would still be capable of doing so.
Skripal and his daughter were found on March 4 unconscious in a bank of streets of British town of Salisbury.
The British news agency Press Association on Friday quoted Sedwill's letter to Stoltenberg as saying Skripal might have been spied on in London.
Moscow has strongly denied responsibility and says Britain is waging a defamation campaign against it.
Mr Yakovenko said: "We still don't have any information about the investigation, we don't have official replies from the British government".