In the letter, Sedwill said the Soviet Union developed fourth generation nerve agents known as Novichoks in the 1980s at the State Institute for Organic Chemistry and Technology near Volgograd under the codeword FOLIANT.
"Only Russia has the means, motive and record", Johnson said.
The Organisation for the Prohibition of Chemical Weapons (OPCW), which collected its own samples in Salisbury at Britain's request, did not assign blame for the attack, in which Russian Federation has denied involvement, or name the chemical agent.
Sergei Skripal has been living in Britain since 2010 but his daughter only arrived last month, to visit her father.
Sergei, 66, remains in the hospital while Yulia, 33, has recovered and been released.
Russian Federation has carried out secret tests on how to smear deadly nerve agents on door handles, declassified British intelligence reveals.
In a statement issued via the police, she said rejected assistance from the Russian Embassy "at the moment".
He said that claim was "extremely suspicious" because the highly volatile A-234 nerve agent could not have been found at the scene in large quantities given that more than two weeks had passed between the attack and the collection of the samples.
Russia's ambassador to the UK, Alexandr Yakovenko, said he had not read Sir Mark's letter but denied the claims in it.
President Donald Trump warned Russia this week of an impending missile strike against its ally Syrian President Bashar Assad over the alleged use of chemical weapons against his own people, although the president subsequently walked back denunciations of Russian President Vladimir Putin for backing Assad. "With no possibility to verify it, the publication by the Metropolitan Police raises new questions rather than gives answers", according to the embassy on its website.
Manchester City crowned Premier League champions
They are in the relegation zone and are more likely to be one of the three clubs to be dropped to the Championship. And by the performance yesterday, they will achieve it in style and break some more records in the process.
200 million eggs recalled over salmonella fears
Anyone who purchased contaminated eggs is asked to return them to the store and get a full refund. At least 22 illnesses related to the eggs have been reported at the time the recall was issued.
Nicki Minaj drops not one, but two new singles
Quavo caught the ire of Nicki Minaj this past week for his supposed involvement in a conspiracy to repress her. It was not the verse it was right now. "With " MotorSport , ' I kinda felt ambushed", she said ".
Hold France orders military action in Syria with US, Britain
The group said it "strongly condemned" the action and accused May of "sanctioning killing" at US President Donald Trump's behest. The opposition leader questioned the prime minister's statement that the Syria attack is " right and legal ".