Or there was no nerve gas to begin with? It's about as easy for the UK's security services to blow the story out of proportion and subsequently plant whatever they need to justify it - as it is for the Russian ones, particularly in this political climate.
Not to mention the string of assumptions that follows even if there was:
1. That it was the russians (the kind of life Skripal led makes enemies left and right)
2. That even if it was russians, it had to be the Kremlin (Putin is not the only game in town in Russia, even if he is the biggest one)
The alternative is that the NHS successfully treated the poisoning by one of the most potent weapons in the world, 5-8 times stronger than VX, which they're barely acquainted with (he should have died before they figured out what it was), have no ready made antidote for, and well beyond the onset of the poison (30s - 2minutes).
Never doubt the incompetence of implementation people.
But wonder if we'll ever find out the truth