During the scuffle with the Doctor it is clear that Tegan's bracelet has no power pack in it.
When the android enters the TARDIS it has the mask on. When the android is seen entering from inside the mask is in the androids hands.
When the android makes his way into Nyssa's room, the room starts to vibrate before she switches on the machine.
When the Doctor shoots the lock with one of Mace's pistols the firing mechanism noticeably doesn't move, making it clear it's a blank-firing prop weapon rather than a genuine flintlock gun.
Despite landing the Tardis on the site of London's Heathrow Airport (some 300 years too early) the Doctor asks Richard Mace where the nearest city is. Surprise, surprise - it's London.