Since the financial meltdown of 2008, China has been the key driver of growth in the global economy. In Beijing, it is easy to see how the country's brand of command capitalism has transformed infrastructure and generated unprecedented wealth. But suddenly confidence has given way to insecurity - at the heart of it is a debt bubble that would threaten the whole world economy if it turned toxic. Hardtalk is in Beijing to speak to Jin Liqun, supremely well connected investment bank chief and former chairman of China's sovereign wealth fund. How worried should we be about the Chinese economy?