An independent inquiry has been demanded into alleged mistreatment of mainlanders detained during the right of abode court wrangle after a survey claimed yesterday they were subjected to systematic abuse. Paul Harris of Human Rights Monitor said widespread reports of mistreatment and the Immigration and Correctional Services departments' sluggish response to the claims justified an investigation by a judge. 'The survey of no less than 90 detainees shows systematic cases of humiliation,' he said. 'Someone clearly told staff to threaten and intimidate people into leaving Hong Kong.' Eighty-two out of 90 mainland overstayers who responded to the survey said they were strip-searched. An Immigration Department spokesman had said strip searches were not routine procedure at detention centres. However, two detainees were searched three times and two more twice, the survey found. Twenty-five said guards tried to pressure them into signing a form volunteering to return to the mainland, the survey said. Numerous people at the Ma Tau Wai detention centre, where survey respondents claimed the worst violations occurred, said guards woke them in the night, demanding they sign. They were told if they did not, they would be blacklisted, personal information would be given to mainland authorities and they would never be allowed to return to Hong Kong to claim right of abode, according to the survey. One detainee at the centre was ordered to squat up and down while naked and a woman was denied sanitary napkins, the survey claimed. Cyd Ho Sau-lan, Frontier legislator, sent a letter and petition to Tung Chee-hwa requesting an independent inquiry. Mr Tung's spokeswoman said detainees should contact the Immigration and Correctional Services departments over complaints. An Immigration Department spokesman said yesterday: 'Perhaps they're not familiar with the procedures. It's a misunderstanding. When they're squatting up and down, it's a part of search procedure.' The respondents were among 179 mainland overstayers arrested after a court ruling that they must return to the mainland before claiming right of abode. They and about 1,000 others are appealing.