Students moved in the flat above us. They regularly stay up until 6am having large gatherings, tv/music on loud directly above our bedroom. We have attempted to talk to them but in return we received threats. I have lost count how many times we have rang the police to no avail. Even the agency we are renting under doesn’t care that we are suffering nevermind that the new neighbours have tampered with our locks.
Contact the environmental health service and insist they come to witness it. They have a duty to investigate. Find out whether they have an out-of-hours service and use it; if not arange alternative visits and installation of a sound recording device. In the meantime you must keep (and maintain) a detailed diary of occurences. If it is regular enough you shouldn’t have too much trouble with it being witnessed. Also contact the university where they are based and explain the situation – write to the Chancellor or vice-chancellor (providing as much detail as possible, including names of the students and their landlord/managing agent).