Ai is aware that his working methods draw comment. When he filled the turbine hall of the Tate Modern with porcelain sunflower seeds last October, 1,600 women in Jingdezhen, the ceramics capital of China, worked for two-and-a-half years to create the work. “It was a huge canvas. There are a lot of political meanings there. They may not even be clear to me. But people will ask: ‘Why did this come from China, why did the Chinese do this, who is involved, how was it achieved, and how much money was involved?’” It has been Ai’s choice to stay in China, and undergo the monitoring and harassment that have forced so many other artists, writers and intellectuals into exile. “It has never been important to stay, until now,” he says. “When I went to New York in 1981, I vowed never to come back.” But he has now become so emotionally involved, and has such faith in the twin powers of the internet and globalisation to change China, that he cannot bring himself to leave.