The politician collapsed on a flight from Siberia to Moscow on August 20 and was flown to Germany, where he was kept in an induced coma in a Berlin hospital for more than two weeks.
Mr Navalny has accused the Kremlin of involvement in the poisoning, which Russian officials have vehemently denied.
In a recent interview with German magazine Der Spiegel, Mr Navaly said he believes President Vladimir Putin was behind it, saying: “I don’t see any other explanation”.
Now British Foreign Secretary Dominic Raab has said that it will work with international allies to take forward targeted sanctions against Russian officials it holds responsible for the poisoning.
The international watchdog, the Organisation for the Prohibition of Chemical Weapons, confirmed on Tuesday that Mr Navalny had been poisoned by a Soviet-era nerve agent from the Novichok group.
It was the same method used in the “Salisbury poisonings” of former Russian agent and British informant, Sergei Skripal, and his daughter Yulia in 2018.
Western governments, including Mr Raab, have demanded an explanation from the Kremlin.
The findings backed those from laboratories in France, Sweden and Germany where Mr Navalny was treated after falling ill on a Russian domestic flight in August.
In a statement, Mr Raab said the UK stood with Germany and France in condemning the “abhorrent” poisoning of the opposition politician.
“Despite having a clear case to answer the Russian authorities continue to make no credible attempt to investigate this attack,” he said.
“There is no plausible explanation for Mr Navalny’s poisoning other than Russian involvement and responsibility for this appalling attack.
“We will work together with our international partners to take forward sanctions targeting Russian officials and others who are considered responsible for this crime as well those involved in the development of the Novichok chemical weapon programme.”