Shortly after the bridge collapses, a wooden support can be seen propping up the TARDIS, revealing it to be backless.
Barbara points off-set to her left, from where she entered the shot, to a strange poster that she has just walked past. The TARDIS, which is standing next to a poster partially visible over her right shoulder, could also be seen next to the off-set poster in the previous shot. The context reveals that the same set was shot from different camera angles to represent different locations - the TARDIS's presence next to both posters is a continuity error.
Wires visibly support the model of the Dalek spaceship. Interestingly, they support the model laterally rather than vertically, presumably because viewers would naturally look above a flying model for strings rather than to the sides.