Trying to Find a SciFi Movie Title

Hello! I've been trying to track down a b/w Sci-Fi movie I've seen on TV only once, back in the early 1980s. I believe it has to be pre-1970 since it is in b/w.

The details I remember about it are:

A man and woman enter a cave in a lightly forested area near an estate (possibly in England) and are transported to a space station far out in outer space, well beyond our solar system. The station has a central hub and a number of long, gantry-like radials from it, I think six or eight of them. The man and woman find black cubes with silver funnels stuck in one end -- these, using earphones, store information about the station, its defenses, and the fact that it has been built to stop an invasion by an alien race. The man and woman manage to launch missles from the station and stop the invasion, then return via the cave to Earth.

Does anyone know the title of this film or any other details about it?