In 2008, Russia's Finance Minister pronounced his country to be an 'island of stability' in the global economic crisis. Since then the rouble has lost a third of its value, the stock market has plunged 70% and the World Bank predicts that Russia's economy will contract 4.5% this year. Igor Yurgens is one of President Medvedev's closest advisers on the economy. Stephen Sackur asks him why Russia has proved so vulnerable.