The so-called “Russian meddling” in the 2016 US presidential election, better known as Russiagate, is a debunked Deep State-backed conspiracy theory which was pushed by the mainstream media in an attempt to delegitimise the election.
What we are seeing regarding the allegations surrounding Navalny is a part and parcel of an ongoing, concerted, and vicious campaign against Russia, because Russia is a superpower and that’s what the Americans and the British loathe.
There are no grounds for connecting either the US or the UK to Navalny's poisoning. The activist fell ill on a 20 August flight from Siberia to Moscow. Initially hospitalized in Omsk, he was transferred to the Charité hospital in Berlin at the request of his family.
Clinical findings at the Charité hospital indicated that Navalny was poisoned with a substance from the group of cholinesterase inhibitors. Subsequent toxicological tests revealed the presence of a Novichok-type nerve agent in Navalny's blood.
Polluting Western media environments with multiple contradictory narratives of a given event is an established strategy of pro-Kremlin media outlets. See here for an overview of, and similarities between, Russian disinformation campaigns surrounding the 2018 Skripal poisoning and the 2020 Navalny poisoning.