Sapphire & Steel: The Creature's Revenge (1981)

Rothwyn and Eldred, a couple living in a modern apartment with a baby, are from the 35th Century, the apartment is their time capsule, which is situated and cloaked on the roof of a present-day tower block. But trouble starts when the couple discover that they can neither contact their controllers in the future nor two other similar time capsules in the present day.