What happens when a professor makes damaging comments about another in front of students? I have had some very negative comments made about me by a small number of students, which my institution is taking seriously enough to terminate my employment. 

I know that a particular colleague has been influencing the students to feel negatively about me, and unfortunately, most of the students I have taught over the past 2 years have been in direct contact with this colleague (sometimes on a daily basis). One course I taught last year actually had fairly good student reviews, and that was because my colleague had nothing to do with those students. In fact, if one looks at my evaluation results from the past 3 years, the students who had nothing to do with my colleague gave me good reviews, and the ones that were in frequent contact with him gave me terrible reviews and made horrible personal, and sometimes offensive comments about me. However, my boss is not willing to consider this and sees only that my evaluation results have taken a downward trend.

In my institution, the lectures are recorded, and I have recently discovered a recording of my colleague talking to my students (who are also his students) before his lecture. In the video, my colleague is heard to make several derogatory comments about me, my teaching, my professionalism, etc., and a student is heard to say "this does not bode well", about the course I was about to start teaching them. This was right at the beginning of the semester and the students did not even know me yet. By the way, the comments made by my colleague were untrue.

As a result of interaction with my colleague, the students were very negatively predisposed to me and made very nasty comments about me and gave me extremely low ratings on their evaluations, which has caused my institution to initiate termination procedures against me.

What can I expect to happen? Has my colleague committed a terminatable offense, and can I expect him to be fired for this?

The way this has turned out is that some students (with whom my colleague also had close contact) complained so badly about me last year that a course was stripped away from me and given to him for this year, and a project that I received research funding for (as the principal investigator) has been taken from me and given to him. He had previously applied for funding for this project and did not inform me or put my name on the proposal (i.e. he was trying to steal my project from me). I have been suspended from work, and forbidden to have any contact with students, for 2 months now.

Of course, the video is from this year, not last year, so I can't prove he did the same last year, so is the one video enough to prove that my colleague has been actively and maliciously sabotaging my career even last year?

Could I still be fired and my colleague kept on after my boss sees what's on the video? That prospect is unthinkable to me, but I have been treated so unfairly so far I could almost see them doing that. I know that my boss likes my colleague and doesn't particularly like me.

Do I have any recourse, legal or otherwise, if, even after seeing the video, my boss fires me and my colleague suffers no consequences?

Thank you.

Further information: I'm in the UK on a fixed contract. My understanding, however, is that they need a good reason not to renew a contract when it runs out.
I am sorry this has happened to you. I have observed this at my place of work too. The poisoned well around you will make you sick. I suggest you get out fast and use our remaining dignity to find someplace where you are appreciated for what you do. Your boss or other colleagues are unlikely to help you because the writing is already on the wall that you are suffering negative consequences of someone else's unprofessional, jealous, petty and just plain bad behavior. Unless you are a mean street fighter, best to dodge this battle and understand that even if you win, this colleague will not change their behavior and likely cause future trouble. Do you really want to face that for the remainder of your career here? As fas as I know, this type of harassment is not protected by laws. Even your friends at work will not want to be involved as they will fear the wrath of this nasty person turning on them, if they speak up for you. I am really sorry. You sound like a sincere person who is doing their job the best they can, but it is hard to contribute well when so much of your energy must be sapped by fighting this stupid battle. Find yourself a nurturing place. The world is bigger than this narrow well.