Neutron-deuteron breakup cross sections obtained within the framework of AGS theory are presented. As input the separable W-matrix representation of the two-body T matrix for the original Paris potential and for a charge dependent modification is used. A criterion to choose an optimal representation based on the Schmidt norm of the kernel of the AGS equations is presented. The results are compared with data from kinematically complete experiments at 10.3 MeV and 13.0 MeV. The neutron-neutron (nn) scattering length is extracted from the cross section of a nn-FSI configuration. It is shown that a reliable analysis of a given experimental situation requires the inclusion of about 400 neighbouring configurations in order to simulate finite energy and angle resolutions. In view of the huge demand on computational resources the simplifying yet very accurate W-matrix method is seen to be an algorithm particularly well suited for such realistic analyses. (orig.).