What has happened to Moscow State Circus? It used to be an old-style, muscle-and-tumble show, energetic and upbeat, lithe and proud, even if it was untouched by every new trend in circus and performance. But that was the former Soviet Union for you, and no one watched the Ruskies for new wave experimentation. Still, that doesn't explain the tired, tatty and just plain hopeless circus show at the South Bank this Christmas.