There is something faintly artificial about the warm atmosphere surrounding the first US-Russia summit of Barack Obama’s presidency, taking place in London this week.

This goodwill was conspicuously absent last year during Russia’s brief war in Georgia, the US’s top ally in the Caucasus. It was missing even in January when Dmitry Medvedev, Russia’s president, greeted Mr Obama’s inauguration by announcing plans for new missiles on the border of Poland, the US’s strongest ally in eastern Europe.