When writing academic work, such as essay and reports, it's important that you acknowledge the books, journal articles, and any other sources you consult in the course of your research. You do this to show your lecturers what you've read, and most importantly to respectfully nod to the work and ideas of other people; this is a matter of academic integrity. Failure to acknowledge your sources implies a) that you haven't done any background reading or research, and b) that all of the ideas you put forward are your own. If you consult sources and draw on the ideas of other people but don't acknowledge them, it's plagiarism. Always, always cite and reference your sources.
Within the School of Law & Government, two referencing styles apply depending on your area of academic focus.
OSCOLA versus Harvard