If the use of a film does not fall under educational fair use, it falls under public use.
To legally screen a film in public it is necessary to have written permission of the copyright holder or purchase a one-time public performance rights license. Sometimes the Addlestone library purchases non feature films with the ppr included. You may contact the Addlestone library to determine if the film was originally purchased with ppr.
Finding and contacting the entity that holds the copyright to a title can be difficult. Often the film distributor from where the film was purchased can sell you the one time performance rights to that title.
If the film was not originally purchased with ppr, you may contact SWANK motion pictures to obtain a one-time performance license. Swank Motion Pictures, Inc.® is a major non-theatrical movie distributor, online CE/CME education distributor and public performance licensing agent in venues where feature movies are shown publicly.
Swank Motion Pictures, Inc.® http://www.swank.com/