The imprisoned Russian opposition leader Alexei Navalny describes himself as a walking skeleton. He’s refusing food in protest at his medical treatment, and thousands of Russians joined protests to show their solidarity. The Kremlin seems intent on destroying Navalny’s movement, irrespective of internal dissent or international condemnation. Stephen Sackur speaks to Vladimir Ashurkov, a key Navalny ally and executive director of his anti-corruption foundation. Is Putin about to eliminate his most dangerous opponent?