The Prime Minister's visit to China was always going to require delicate navigation. The Foreign Secretary set trade as a priority for British diplomacy, and there are few countries where the gap between the potential for trade and the UK's actual performance is as wide as it is with China. But it would also be unconscionable for Mr Cameron to drum up more trade, while playing down China's egregious violations of human rights. How he balances the two will say much about the character of his government and his leadership.

In the event, circumstances have conspired to push the human rights situation further up the agenda than Mr Cameron and his advisers might have hoped. His visit not only follows the award of the Nobel Peace Prize to the imprisoned dissident, Liu Xiaobo, (and Beijing's angry response), it comes as the authorities are upping the pressure on the artist, Ai Weiwei. Mr Ai has a British connection, too: as well as helping to design Beijing's Bird's Nest stadium, he created the sunflower-seed installation now occupying the Turbine hall at London's Tate Modern.

Silence on human rights should thus be no option; Mr Cameron should make clear to his Chinese hosts where he, and Britain, stand. In one way, the low level of trade should make that easier. The UK has been less successful than other European countries in capitalising on China's spectacular growth. We remain buyers more than sellers; British companies would have less to lose if China cut up rough.

Yet Mr Cameron has invested a great deal in this visit. As when he went to India in July, he is taking a large delegation of ministers and business people. And it is refreshing to see a British Prime Minister combining politics with business, as the US and our European partners habitually do. It would be equally refreshing, though, to hear some plain-speaking from a British Prime Minister on human rights. Beijing's international economic clout has too often given its leaders a free pass to engage in repression at home. The difference this time is that, even if Mr Cameron's courage fails, Beijing can no longer hide its true face; with Liu Xiaobo and Ai Weiwei, its excesses are there for all to see.