PRELIMINARY hearings against four former National Mutual Asia (NMA) agents are expected to start within weeks. Sources close to NMA said writs alleging a conspiracy against NMA by former managing director Andrew Yang Fan-shing and three other senior staffers who quit the firm in January should reach the courts shortly. Writs were filed against Mr Yang and colleagues Hans Lee Ho-sang, Inneo Lam Hau-wah and Raymond Chau Siu-ping at the end of January alleging they ''combined together to injure the company'', according to the firm. NMA is seeking an undisclosed amount in damages from the men. In May, the company said the defection of Mr Yang and 650 salesmen had cost it $30 million. NMA used corporate detectives Kroll Associates to investigate the resignation of Mr Yang. The detective firm is understood to have investigated whether departing staffers took secret company information with them when they went. Kroll was hired as part of a crisis plan as NMA struggled to work out how many agents were leaving and how much business they controlled. Findings outlined in Kroll's confidential report are understood to have formed the basis for some of the allegations against Mr Yang and the other former NMA staff. The other men named in the writ all held senior positions. Mr Lee apparently quit NMA in December 1993 shortly before Mr Yang quit, saying he planned to retire to Australia. Mr Lee held the post of chief general manager while Mr Lam and Mr Chau were sacked by the firm on January 24 - three days after they handed in their resignations. Meanwhile, a spokesman for the Securities and Futures Commission yesterday said it would co-operate with police in their investigation of executives of Top Glory. He said: ''Police are handling investigations. If it [becomes] apparent that there were any violations of securities regulations, then we [will] co-operate with the police. But at this stage they have not come to us. We will have to wait and see what happens.'' The stock exchange said it was ''always concerned about any listed company being investigated by the police.'' However, it refused to comment on an investigation into an individual company. Meanwhile, the Insurance Commissioner looks set to change the rules on the ''twisting'' of policies in the wake of issues raised in the NMA issue. Twisting is when an insurance agent persuades a customer to drop one policy and buy another. In the past, only an insurance agent's current employer has been able to file complaints with the commissioner even though a new employer might not be aware that clients of a previous employer were being twisted.