It is impossible and wrong, in this fascinating exhibition on Russian art between 1917-1932, to separate art from politics, utopian propaganda from dystopian tragedy. Aesthetic judgement is inevitably compromised. Some may think it obscene to celebrate this period in Russian art: yet it is surely right to make us confront it, to see the boldness of the art and to try and fathom the mixed motives, the hopes and fears and struggles of the artists involved. Right too, when the headlines are full of Trump and Putin, to remind us of the history. By Jenny Uglow.