Since I'm building a prop from Space 1999, it seemed appropriate to have a quick look to see if there was anything on YouTube covering the special effects. This first film is interesting showing how basic a the "in camera" shooting techniques were, and how effective the results.
Mind you, how long is it since you could "buy a kit for a pound"!
Interesting that there were many railway models in there. The girder bridge? Sounds Airfix to me.
There's also this film, which I've shown before, but it's worth a second look.