Mr Navalny was detained at a Moscow airport on Sunday after spending five months in Germany recovering from nerve agent poisoning that he blames on Moscow.
Mr Navalny was poisoned last August and collapsed on an internal flight in Siberia, and he was flown to Germany for emergency medical treatment.
President Vladimir Putin's government denies poisoning Mr Navalny.
Cabinet minister Dominic Raab tweeted: “It is appalling that Alexey Navalny, the victim of a despicable crime, has been detained by Russian authorities. He must be immediately released.
“Rather than persecuting Mr Navalny, Russia should explain how a chemical weapon came to be used on Russian soil.”
Mr Navalny’s detention has been condemned by governments around the world, with the European Union, Germany and the US all speaking out about the arrest.
US secretary of state Mike Pompeo said he was “deeply troubled” by Mr Navalny’s arrest, while adding a veiled criticism of Russian president Vladimir Putin.
“Confident political leaders do not fear competing voices, nor see the need to commit violence against or wrongfully detain, political opponents,” he said.
Prior to Mr Navalny’s arrival at Moscow’s Sheremetyevo airport, Russia’s prisons service said the 44-year-old has violated parole terms from a suspended sentence on a 2014 embezzlement conviction.
Officials said he would be held in custody until a court rules on his case.
Tom Tugendhat, the foreign affairs select committee chairman, said Russia’s justification of Mr Navalny’s arrest was “designed to deceive”.
“Navalny missed probation hearings because he was recovering after the same Putin officials who ordered his arrest tried to murder him,” the Conservative MP tweeted.
“If he gets beaten up and there are marks on the weapons, they’ll charge him with damaging Government property.”
Shadow foreign secretary Lisa Nandy said: “Alexei Navalny was the victim of a cowardly chemical weapons attack. He has shown great courage in returning to his homeland.
“His detention is unjustifiable and an insult to the Russian people. He must be released immediately and his attackers brought to justice.”
Meanwhile, Labour MP Catherine West called for a co-ordinated response from the UK Government, the European Union and the incoming Joe Biden administration in the US.
SNP defence spokesman Stewart McDonald was equally forceful in his condemnation of Mr Navalny’s arrest.
He wrote on Twitter: “Having failed to crush Navalny’s bravery with poison the Russian government will now try, and fail, by putting him in prison.
“The free world must stand in unison in calling for his release. Those who continue to shill for Putin’s various outlets must surely feel shame tonight.”
Defence committee chairman Tobias Ellwood called Mr Navalny’s decision to return to Russia “incredibly brave”, in a sentiment echoed by veterans minister Johnny Mercer.
Mr Ellwood said: “Poisoned by the FSB yet he chooses to return to Russia and has now been arrested.
“Incredibly brave stand by Navalny in the name of democracy as we head towards Russian parliamentary elections.”
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