10 Behind The Scenes Secrets From Doctor Who: An Unearthly Child
4. The TARDIS Fell Victim To Budget Cuts Very Early On
Doctor Who was originally conceived as an educational show. This accounted for the roles of Susan's two teachers. Ian Chesterton was a science teacher, while Barbara Wright was a history teacher. The Doctor would take audiences through time and space, helping them understand various new tricks.
The TARDIS then would be a part of this, with the ship's chameleon circuit allowing it to take the form of something that would be relevant to each different story. However, the production team quickly realized that this was unlikely to be much of a runner, as the cost involved in creating a new prop for each new serial was sure to spiral out of control.
So, for An Unearthly Child, it was decided that the TARDIS had a faulty chameleon circuit. This would explain why, having chosen the form of a police box, it remained that way forever. Later incarnations added extra levels to this, including perception filters, while in the very beginning, the police box looks perfectly at home in the junkyard. Admittedly, it looks a little less at home on the barren wasteland that the episode ends on...