If UK were able to determine what substance were used to poison that people, they should have known about it existence and have samples of it. But supposed agent weren't added in Chemical Weapons Convention (CWC), that means UK hid it from them, violating statements at article 4 of CWC.
First of all, we still not know if there really was a "nerve agent poisoning" at all.
Other than this, you can be sure that the British have samples, at least since the time the US dismantled USSR´s Nukus labs. I´m not that deep into the intricacies of CWC treaties, but it seems that certain labs may legally keep "small" quantities, formulas, and production methods of those agents for reconnaissance purposes.
Or mrs. May now may change her mind and say that there was no new chemicals there and whole accusation were just a small mistake.
Both ways it's not what brilliant politicians should do.
The British government is obviously not telling the truth. Either, the British government is actively involved into the case, aiming at further undermining Russian credibility, limiting it in the middle east and elsewhere
. Or some British circles are trying to get rid of Mrs May. Or some other foreign agency outside Russia (Israel had been mentioned, for retaliation of Russian support of Syria, screwing up its plans).
What was the motif of that "assassination"? That's not right time (right before "election") nor victim (he wasn't a threat to Russian government anymore, after he tell about his foreign contacts).
In addition, there seems to exist an inofficial agreement, to abstain from any retaliation means against exchanged enemy spies.
But who would want that anyway? There is no killing without motif (well, except maniacs, but that's not about this case).
Maybe Skripal was still involved in other (non-Russian) activities. Probably still with ex-MI6 agents (names are known) and also been involved in the "dirty dossiers" campaign against Trump.
At the moment, it seems that european politicians are starting to slowly redraw from any "unlimited support" of the British government.
I find that funny who of all leaders congratulated mr. P.
Well, German tv is commenting the Russian election as "undemocratic", gives much room to osce´s nitpicking, and continues to praise Navalny as the better solution. So, nothing new, panic at best.