It sounds like "Quartermass and the Pit" aka "Five Million Years to Earth." I mean, that is the literal ending of the movie. Problem is, QatP is in color. Possible answers include:
1: There was sometiming wrong with your reception and/or set. That, or it was a Black and White.
2: You were watching the serial QatP, which the movie was based on.
Either way, I think QatP is right. There is a review of the movie with images at
http://www.stomptokyo.com/movies/q/quatermass-and-the-pit.html. Check it out and see for yourself