I remember seeing this broadcast. It was made by Euston Films so I was expecting th usual "Sweeney" type over-grain in the picture (1970's high speed 16mm), but instead it had the full gorgeous look of a motion picture, having been shot in 35mm with full motion picture negative (whereas most American productions were shot on 35mm television stock). The special effects where not all that good where the space shots were concerned - even by 1970's standards (to see good examples of these effects look at Space 1999 (1976 - 1978) whose Director of Effects, Brian Johnson, went on to win an Oscar just a couple of years later - for Alien). But the idea that a beam would come through space and consume vast number of people and turn them into a diaphanous web was effectively executed. It would be nice to see it again in its full version - perhaps the BBC could show it without breaks in two parts. Also it was an early appearance for Simon McQuorkindale (Manimal!).