By Caroline Gluck BBC, Taipei

Mr Chao has denied the allegations

The son-in-law of Taiwan's President, Chen Shui-bian, has been detained by prosecutors after a night of questioning over allegations that he was involved in insider trading.

It is the first time a member of the family of a Taiwanese president has been detained on suspicion of breaking the law.

The case, which has prompted calls by opposition politicians for the president to resign, has dominated the news headlines.

TV footage showed the president's son-in-law, Chao Chien-ming, being escorted into a police van and taken to a detention facility on the outskirts of the capital.

Mr Chao's parents, brother and sister-in-law were also questioned but later released.

It has been alleged that Mr Chao and his family made windfall profits on shares in a state-owned property development company using their ties to the president to obtain privileged information.

Mr Chao has rejected allegations of insider trading.

Scandals mount

The case has sparked calls from some opposition politicians for President Chen to resign. It has also angered many within his own party, which had prided itself on its clean image.

President Chen, whose popularity ratings are at an all-time low, apologised to the public as he marked his halfway term in office at the weekend.

He said he respected the judiciary's independence and would not cover up wrong-doing.

But the scandals appear to be snowballing. Earlier this week a cabinet official - the vice chairman of the National Science Council - resigned after being arrested on charges of illegally profiting from an engineering contract.