The effect of the monster inside Westminster Abbey was achieved by using a pair of gloves covered in fake foliage stuck through a blown-up picture of the Abbey interior.
Nigel Kneale was still writing the final episodes when the first episode was broadcast, and had only a vague idea how it would end.
The serial's storyline concerns the first three humans to journey into outer space and to orbit the Earth. John Glen plays the major role of Dr. Gordon Briscoe. On February 20, 1962, almost nine years later in real life, his near namesake John Glenn became the fifth person in space as well as the first American to orbit the Earth. He was the second person overall to orbit the Earth after the first person in space, the Soviet cosmonaut Yuri Gagarin on April 12, 1961.
Broadcast live, this was the first BBC Drama to be recorded onto film via the 'telerecording' or 'kinoscope' process. Telerecordings were made by filming the image off a specially designed TV screen with a film camera (either 16mm or 35mm.) Unfortunately, the results were judged to be unsatisfactory, and only the first two episodes were recorded, the rest being broadcast live. Because of this, only the first two episodes were preserved.
When BBC research revealed that 75% of the audience for the final episode had viewed all previous episodes, scepticism about the viability of a TV drama serial for adults was overcome, and the format went on to become a staple of TV programming in the UK and elsewhere.