Liu Xiaoming: How will China respond to unrest in Hong Kong?

Is Chinese leader Xi Jinping facing the most serious challenge of his presidency? The significance of the political unrest in Hong Kong stretches far beyond the borders of its territory. If Beijing cannot quell the calls for freedom in Hong Kong, what does that tell us about the sustainability of its authoritarian rule elsewhere? Stephen Sackur speaks to China’s Ambassador in London, Liu Xiaoming.