like the other reviews-I was 9 when this series was broadcast in summer1962.It scared me stiff(it was on quite early in the evening).
There are some elements I vividly remember; -newspapers with headlines like "Have you seen these men?" -a scientist being "taken over" by the force and being hurled over a landing.When his face was shown he was dead with mouth/eyes wide open .I was terrified! - the ending; Scientists had worked out that the people taken over by the force had assembled in an aircraft hanger. It was vital to kill them all by a specified time-otherwise the force would expand exponentially.An RAF jet bomber was sent to bomb the hanger but it did so too late!! The series ended with the observers by the hanger panicking and being taken over by the force.
When I went to bed I couldn't sleep. Unfortunately all tapes have been lost.Pity-I'd love to see it again.