Foreign Secretary James Cleverly suggested the latest jail sentence was an attempt to silence dissent.
Britain has demanded Russia releases Kremlin critic Alexei Navalny after he was sentenced to a further 19 years’ imprisonment on charges he rejected as politically motivated.
Foreign Secretary James Cleverly said Moscow’s “abuse” of the opposition leader shows a “complete disregard for even the most basic of human rights”.
Mr Navalny, already serving a nine-year term, was handed nearly two decades’ more following a behind-closed-doors trial in a penal colony east of Moscow.
Appearing gaunt in court but displaying a defiant smile, the 47-year-old was convicted of extremism charges relating to his anti-corruption foundation.
Mr Cleverly tweeted: “Alexei @Navalny has been sentenced to an additional 19 years in a Russian prison.
“His abuse shows Russia’s complete disregard for even the most basic of human rights.
“Dissent cannot be silenced. The UK calls for his immediate release.”
One of president Vladimir Putin’s loudest critics, Mr Navalny’s arrest in 2021 came after he returned to Moscow following a period of recuperation in Germany after being poisoned by the Novichok nerve agent.
Mr Navalny denied the charges and warned ahead of the verdict he would be handed a “Stalinist” prison term to ward off other dissenters.