I'm preparing for some seminars next week but I really want to show the students a film which they have been recommended to watch. I doubt any of them will have done it in their own time. The film is two hours long which will fill the seminar. I'm feeling guilty that I am being paid to teach but won't actually be doing anything if they sit watching the film. I'm happy to stay behind for discussions if they are though.

Hey!
I know proper lecturers who show films in lecture-time rather than 'lecturing'. In fact this year one of them couldn't get the video to work so just cancelled the class. The students may not necessarily see the value in it, so it would be worth allocating other formal time to discussion; or, even better, posing questions for them to think about whilst watching it

You could pose some questions at the start - then halfway through the film have a brief coffee/toilet break and before starting the film ago, repose the questions, and try and get them on track for the rest of the film. Then any brief questions at the end...

I don't think you are being lazy Pamw, but do you think that a student (assuming undergraduate) could be truly attentive and engaged throughout a 2-hour film?  I know that in my university this would not be possible, especially with the prospect of a discussion at the end! I think that you are asking a lot from them.  Couldn't you split it up over a few weeks? I am sure they will learn more if it were shown in bite-sized pieces!  Good luck!

Do you need to show the whole two hours? If it's a DVD it might be possible to just select maybe 45 minutes worth of chapters that cover the main points. You could introduce the chapter, provide the context then discuss after the chapter.