Revealing mistake: During the first major Zulu attack, a warrior leaps down from the rampart and faces a British soldier (near the bottom right of the screen). The soldier lunges with his rifle and it's all too visible that his bayonet stabs to the side of the Zulu's chest.
Continuity mistake: When the Senior Civil Servant is reading Dowding's letter there is a knock at his door. In the next frame the Civil Servant has removed his glasses, appears more leaned back in his chair, and the position of the letter/page has also changed. (00:06:00)