This is a demo of a planned game called '3D Wars', written by Nick Pelling (aka Orlando) who produced some of the best games for the BBC Micro. This game was never released or finished, but the demo was given away on the cover tape for the December 1984 issue of 'Personal Computer Games' magazine.
There is relatively little gameplay as such in the demo, as it appears collision detection hasn't been implemented.Your ship can move around the bottom portion of the screen, and fire at the oncoming alien ships as the 3D 'tunnel' zooms past you. However you don't appear to be able to destroy them, nor can they harm you when they get to your end of the tunnel. Also only some sprites have been finished, so others are just flickering black blocks. There's no score or instructions, or indeed very much point at all...