Revealing mistake: Just before the doctor and his companions step out of the TARDIS into 21st century London you can see the reflection of the outside of the TARDIS windows on the blue velvet curtains.
Revealing mistake: When the red Dalek falls down the shaft, there is a very clear shot of its base with three small furniture casters (though it must be a dummy, as there is no hole for the operator's feet to protrude).
Revealing mistake: On the left hand 'Roboman Converter' two of the top row of red lights are not working.
Revealing mistake: When the Red Dalek and the Dalek Supreme fall down the mine shaft, they have been replaced with obvious models that don't resemble the Dalek's image (i.e. larger necks; more skirt balls; thinner dome lights).
Revealing mistake: When the van rams through the ranks of blue/silver Daleks in the street, some of those knocked flying are seen to be completely empty casings.
Revealing mistake: When the workers are running away from the mine before it explodes, one of the female extras (the woman wearing the blue shawl) suddenly slows down to a relaxed stroll - obviously thinking she's safely out of shot.