The Home Office must update Detention Services Order 03/2015: Handling of Complaints to clarify that, in investigations carried out by the Professional Standards Unit into allegations of serious misconduct against contractor staff: Professional Standards Unit investigators must carry out interviews themselves and not rely on contractors to do so. All staff against whom allegations are made must be invited to interview. Where there are inconsistencies between any accounts given of events, any evidence relating to those accounts (including footage and documentation) obtained by an investigating officer must be shown to the complainant and to the subject of the complaint, prior to reaching a conclusion. The Professional Standards Unit must be given information about previous complaints made against alleged perpetrators, including unsubstantiated complaints. Previous disciplinary action against alleged perpetrators must be taken into account. Investigators must look for evidence that is both supportive and undermining of the complaint. Full reports must be sent to complainants (and their solicitors if applicable). Investigation reports and/or outcome letters must be sent directly from the PSU to complainants (and their solicitors if applicable). The Home Office Professional Standards Unit must ensure that training about the updated guidance takes place on a regular (at least annual) basis for staff dealing with investigations, as well as those responsible for managing them. The training must be subject to an assessment. The Professional Standards Unit must also review the training provided to investigators and ensure that investigators receive regular and adequate training, from a variety of perspectives, on issues including: the nature of immigration removal centres and issues that may arise; obstacles that detained people may face in making complaints; interviewing vulnerable witnesses; and use of force and assessing reasonableness of force.