Remember that Inter-library loans may only be cancelled by the British Library or other lending body. Photocopies are yours to keep. Most other items are issued for three weeks. It may be possible to extend the loan, but you must bring the item back to the library site from which you borrowed it, it can then be checked to see if a renewal is possible. Any item recalled by the lending library, after the initial three weeks, must be returned immediately, regardless of the due date on slip cover.
Theses are for reference only and are usually supplied on microfilm.