Ai Weiwei is both one of China's best-known artists and one of the governments highest-profile critics.

The artist has spoken out against human rights abuses and urged Beijing to reform its political system.

He has been held at a secret location since his arrest for suspected 'economic crimes' in April 2011.

Before he was detained he sent many of his works to a major exhibition which has opened in London.

Carol Yarwood of the BBC's Chinese Service reports.