'He said police lashed him with a whip and I saw black and blue marks on his arms.'

She said she submitted an application for a medical examination to the Yixing People's Court yesterday to demand a check-up for her client.

Wu, 39, has spent large sums over the past 16 years collecting evidence of pollution from about 2,000 chemical factories in Yixing which are contaminating Tai Lake, the third-largest freshwater lake in China.

The efforts were part of his push to get the government to clean the lake, once a famed beauty spot. In March, Wu alerted the media to contamination of many reservoirs in Yixing, where hundreds of thousands of residents have been forced to buy drinking water.

The ecological warrior claimed to have suffered two broken ribs after being beaten up three times in 2003 by men hired by chemical factories.

Earlier this month, his wife, Xu Jiehua , filed a lawsuit on his behalf in a Beijing court against the State Environmental Protection Administration's decision to name Yixing one of the mainland's 44 'Green and Eco-aware Cities'.

He had planned to lodge the application himself but was arrested in mid-April for alleged blackmail. He is due to appear in court on June 12.

The indictment against him alleges he wanted to expose Tai Lake's pollution to blackmail the government. It said Zhoutie township's party secretary, Wu Xijin , paid the campaigner 40,000 yuan.

But Ms Xu said the officials had set a trap to stop her husband's campaign. She said they gave him the money to cover expenses on his trips to Beijing, Guangzhou and other cities to attract investment.

'What worries me now is my husband's safety,' she said. 'He was nearly beaten to death.'