UNITED Democrat Lau Chin-shek is to write to the Secretary for Security Alistair Asprey today asking for more details on the investigations of political groups. Mr Lau said he wanted to know what sort of information the Government had collected on him. Mr Asprey has admitted the existence of a Standing Committee on Pressure Groups from 1977 to 1982 to ''gauge public opinions and aspirations'', but denied it carried out political investigations. But Mr Lau said he did not believe the administration had never conducted political investigations. He was concerned about the treatment of the information after 1997 - whether it would be destroyed, passed on to China, or returned to the people involved.