After chemical weapons were destroyed in Russia [which was confirmed by the Organisation for the Prohibition of Chemical Weapons (OPCW) in 2017], its development continued in the United Kingdom itself as well as in the Czech Republic and Sweden. Following the collapse of the Soviet Union, the laboratories for the production of above-mentioned class toxic agents remained in a number of other countries, including in the Baltic states.
No evidence given. The nerve agent has been identified as Novichok (which means newcomer in Russian). It is known to be more powerful than VX and was developed in Russia in the 1970s and 1980s https://www.voanews.com/a/british-prime-minister-russia-poisoning-spy/4294683.html. It's so unusual, that very few scientists outside of Russia have any real experience in dealing with it and no country outside of Russia is known to have developed the substance https://edition.cnn.com/2018/03/13/europe/what-is-novichok-nerve-agent-intl/index.html
The Minister of Foreign Affairs of Sweden forcefully rejected the allegations, and so did the competent authority on the topic in Sweden (the Swedish Defence Research Agency). https://www.svt.se/nyheter/utrikes/ryssland-giftet-som-anvandes-mot-skripal-kan-ha-kommit-fran-sverige. Later on, the Russian ambassador to Sweden stated that it was "a guess" without any facts supporting it https://www.svt.se/nyheter/utrikes/ambassadoren-backar-efter-giftutspel.
Also the Czech Foreign Minister Martin Stropnicky on Saturday denied accusation that the nerve toxin used against a former Russian double agent and his daughter in southern England came from the Czech Republic. https://mobile.reuters.com/article/amp/idUSKCN1GT0ML?__twitter_impression=true
In its statement, the European Union expressed shock at the offensive use of any military-grade nerve agent, of a type developed by Russia, for the first time on European soil in over 70 years. http://www.consilium.europa.eu/en/press/press-releases/2018/03/19/statement-by-the-foreign-affairs-council-on-the-salisbury-attack/