apparently, there's a shortage

The new Doctor Who series has a need for dwarf midget little people as actors for various extraterrestrials. They’re running into a couple of large problems:

Bosses wanted them to play tiny blue aliens - but most have been snapped up for the new Charlie and the Chocolate Factory movie and to play Gringotts Bank staff in the new Harry Potter film. Dr Who executive producer Russell T Davies said: “It’s very difficult to employ persons of restricted growth when, as our producer Phil Collinson says, `Bloody Gringotts and the Chocolate Factory are filming at the same time’.

I doubt the people who made The Terror of Tiny Town had these problems.
Via DDTB