According to Russian media reports, Andrei Sidelnikov was given a travel ban by Russia's Federal Security Service late last year. However, he managed to leave the country via Belarus, which has a free border with Russia, then made his way via Ukraine to Britain.
The group said on its website: "The British government has granted... Sidelnikov political asylum. We see this as an acknowledgement that present-day Russia is not a democratic country, but a country where rights and freedoms of its citizens are not respected, a country where people are persecuted for political reasons."
According to the Russian news website Lenta.ru, Sidelnikov was questioned by the FSB in connection with the October 2006 murder of investigative journalist Anna Politkovskaya, and met with Russian security service defector Alexander Litvinenko days before his fatal poisoning in November 2006.
The leader of the group, which translates its name as "It's Time!", was arrested several times at unsanctioned opposition marches.
The group's statement said: "The Pora movement expresses full gratitude to the British government for granting political asylum to our leader. We are glad that Britain is faithful to democratic principles, despite political end economic pressure from Russia's authoritarian regime."
