Death Angel - Theatre Box / Drama Rama (1981)
 

One of the scariest things I ever remember seeing (and didn't think I would ever get the chance to see again) on children's TV, they simply don't make them like this anymore. The cherry on top is that it was written by and stars Brian Glover and also features a young Ray Winstone.

Sit back, relax and enjoy.

http://www.youtube.com/watch?v=PogTk7qhebM