When Liu Xiaoming agreed to come on the Andrew Marr show, he ought to have expected that – as the Chinese ambassador – he’d be asked about Uighur Muslims. He doubtless came on to bemoan the Huawei decision. But as anyone with a social media account could have told him, video footage of people with their heads shaved, blindfolded, kneeling, handcuffed, being forced on to trains have been circulating widely for days now.