What was the first Doctor Who spin-off television series?

The first Doctor Who spin-off television production was K-9 and Company. Its pilot episode, “A Girl’s Best Friend”, was broadcast by BBC1 as a Christmas special on 28 December 1981.

The programme reunited two popular former companions: Sarah Jane Smith, played by Elisabeth Sladen, and K9, the robotic dog voiced by John Leeson. In the story, Sarah and K9 investigate the disappearance of a young man in the village of Moreton Harwood while rumours of witchcraft spread through the community.

There is an important technical distinction behind this answer. K-9 and Company was a pilot for a proposed continuing series, but the BBC did not commission further episodes. It therefore became the first Doctor Who spin-off to reach television, even though it never developed into a full series. The later Sarah Jane Adventures, which ran from 2007 to 2011, was the first successful ongoing television spin-off centred on a Doctor Who companion.

The pilot attracted about 8.4 million viewers. Its failure to continue was linked partly to a change in BBC One management and opposition from the incoming controller.