While I agree that the Tories are a pile of lying shits, it's also true that Putin is laying piece of shit who's quite capable of doing exactly what he's been accused of. It is possible for both sides to be the bad guy here.

Russia's denials have been of the implausible deniability  variety, so it appears to suit them to have everyone believe it might well have been them.

Since it looks like assorted governments who might not be enthusiastic about action against Russia have decided that the evidence they've seen  is strong  enough to take diplomatic action I suspect the mostly likely scenario is that Russian government was involved, at least to the criminal negligence level, possibly directly.