Ah well. I had an interesting interview lined up for tomorrow, but it was not to be. The Chinese authorities, in their wisdom, have prevented Mo Shaoping – the lawyer for Liu Xiaobo, the Chinese dissident who won the Nobel Peace Prize – from leaving China.

He and his colleague Professor He Weifang, who was also stopped at the airport, were supposed to attend a meeting in London of the International Bar Association. The police who detained them said their leaving could be “a threat to China’s national security”.

The meeting was about how difficult it is for lawyers in China to be independent of the Communist Party. Judges are chosen by party leaders, and there is no separation of powers.

“Only a small minority of lawyers in China have become involved with civil and political rights or broader public interest cases, and they are increasingly the targets of intimidation and abuse,” says the IBA.

“The need for judicial reform is another factor affecting both the legal profession and access to justice for the Chinese population.”

Mo Shaoping represents – or tries to represent – many of China’s leading dissidents when they appear in court. When I have interviewed him in the past, at his office near Tiananmen Square, he has carefully stuck to legal matters, explaining how the supremacy of the Communist Party is an obstacle to the rule of law.

He said today he believes they were barred from leaving because the Chinese authorities suspected that instead of going straight home from London, they would go on to Oslo to attend the Nobel Peace Prize award ceremony on December 10th. Liu Xiaobo can’t pick up the prize himself because he is in prison. His wife, Liu Xia, was put under house arrest after the announcement, so she has issued an invitation to 140 friends and supporters to go in their place. So far, only one – the environmentalist Dai Qing – is out of China and able to attend.

Why are the Chinese drawing more attention to their poor human rights record just as the British Prime Minister flies to Beijing? There are a couple of explanations. First, the right hand doesn’t know what the left is doing – the decision to stop Mo and He at the airport was taken at a low level. I doubt that. More likely, the Chinese government has calculated that it can stand the international heat. Yes, Mr Cameron will ritually refer to the “UK China human rights dialogue.” Yes, the western media will pounce on the story.

But Britain and America need the buoyancy of the Chinese economy if they’re to recover from recession, so the Chinese feel they can assert themselves without few worries about international opinion