this is believable because Russians are renown at the arts and sciences of the poison craft and they usually don't fail.Well done NHS - but it has not been established who did the poisoning.
It is remarkable that the poisoning took place only 8 miles from the Porton Down establishment. My immediate thought was a false flag operation using a sample from Porton Down.
Blaming Russia was convenient but was not confirmed. In fact the UK Foreign Secretary was caught lying.
i once worked with a Russian asylum seeker (She is a software engineer) who said there is a saying in Russia concerning certain widows
"how did her husband die? No one knows, and he had a good dinner of mushroom soup that night."