Most major cities have at least one festival of some kind, not to mention the many festivals in small towns and remote areas. Film festivals vary hugely in the kind of work they screen (from shorts to features, documentaries to experimental films) and the platform they provide for your work. It is important to do some research and approach festivals with programming and selection policies appropriate to your work. As many festivals are dedicated to mainstream film or video work it is generally not worth submitting your film unless you believe your work fits in with their rationale or program. Most festivals are clear about the type of work they accept and state it in their submission guidelines. But you can also get an idea of they type of work a festival supports by looking at their previous programs.
For further guidance on approaching festivals we recommend the LUX Distribution Guide which contains excellent advice on how to show your work in the best light for festivals and their programmers.
This festival section is broken down film and video festivals in the UK and in the rest of the world: