"We have information indicating Russian intelligence service interest in the Skripals dating back at least as far as 2013, when email accounts belonging to Yulia Skripal were targeted by GRU cyber specialists", he said.
The report also says that the nerve agent used to poison the Skripals was produced in Russia's Shikhany military research center, which ran a chemical weapons program with the codename Foliant.
Investigators from the Organisation for the Prohibition of Chemical Weapons (OPCW) said the nerve agent was "of high purity".
Mark Sedwill made the assertion in a letter to NATO Secretary General Jens Stoltenberg explaining Britain's conclusion that the Russian government is to blame for poisoning the Skripals with a military-grade nerve agent on March 4.
Britain blames Russian Federation for the March 4 poisoning of Sergei Skripal and his daughter Yulia in the English city of Salisbury. "There is no plausible alternative explanation".
Sir Mark said: "There is no plausible alternative explanation", adding that Russian Federation had continued to produce and stockpile small quantities of Novichok within the last decade.
Sedwill said "only Russian Federation has the technical means, operational means and the motive" to carry out such an attack.
Sergei Skripal remains in hospital in serious condition, while Yulia Skripal has been released.
Although Russia signed the worldwide Chemical Weapons Convention, it continued to "produce and stockpile small quantities of novichoks [nerve agents]", Sedwill claims in his letter.
The global chemical weapons watchdog has said an analysis of samples gathered from Sergei Skripal, Yulia Skripal, and detective sergeant Nick Bailey - who was affected during the emergency response - confirmed the U.K.'s assessment of the incident.
Russian Federation denies the British claims about Novichok, saying that it completed the destruction of all its Soviet-era chemical weapons arsenals a year ago under global oversight. The strongest concentration of the Novichok nerve agent found in the Salisbury incident was on the front door of Mr Skripal's home.
On Wednesday, during the UN Security Council meeting, Russia's UN envoy Vasily Nebenzya noted that Skripal, who had been convicted of spying, served his sentence and was pardoned.
She said she had declined an offer of assistance from the Russian embassy "at the moment".
Russia has "a proven record of conducting state-sponsored assassination", Sedwill wrote, citing as an example the 2006 poisoning death in London of Alexander Litvinenko, a former Russian spy.
"We have every reason to believe this could be a question of the deliberate, forcible detention of a Russian citizen or possibly their coercion into a staged announcement", foreign ministry spokeswoman Maria Zakharova said.