They Might of but i would say no as Russia has been slandered and accused of things without proof over the last years with the US Elections sabotage (never true), they are continually banned from sports events for "alleged doping". The UK government is blowing this Nerve Agent Attack out of proportions and are only worsening global relations with Russia. There was no outrage or crisis over Kim Jong Nams assasination which was conducted with the deadliest Nerve Agent VX and in a crowded airport where many could of been killed if the Agent had spread and this event was not dramatised as much as the Skripal case.
The UK says it has strong Evidence that Russia conducted the attack as a "Military Grade" "Novichok" series Nerve Agent was used. Well i have fair knowledge in the fields of Military and Weapons and i can say that the Novichok series of Nerve Agents are among the most lethal in the world and are 6-8x more lethal than VX.
I do not know why Theresa may is using "military grade as a term" as all Nerve Agents are Military grade and the one in this attack didn't seem military grade at all and more likely a crude nerve agent due to it making all the affected ill instead of Dead especially Skripal and his daughter after direct exposure, Of it was a Novichok agent they would be Dead. The Truth is Nerve Agents are not hard to make or acquire, Its fact that many commercial pesticides are watered down Nerve Agents and some even have the same side effects and molecular structures just not as lethal, they are just not weaponised like Military grade Nerve Agents with additions of certain chemicals. With this information it can be made clear that it is possible that a non state actor may of commited the attack such as Terrorist Groups or even ex KGB syndicates that may hold grievances.
Again it may be Russia but until solid evidence and a detailed investigation can take place proving their involvement we can't accuse anyone this soon with brief and inconclusive evidence.