Continuity mistake: Harry Palmer uses the leather wrist restraints to lacerate his wrists - the pain enables him to resist being involuntarily hypnotised. The next time he is woken roughly by the guards for another hypnosis session, his wrists are unmarked.
Other mistake: When Palmer raids the factory in search of Radcliffe, he summons a Land Rover to break down the warehouse door with a silent wave of his hand, but the Land Rover appears from behind a corner and therefore could not have seen him.
Continuity mistake: While a prisoner, he grows a stubble. Upon escaping in the telephone booth, he is clean-shaven, but subsequently regains his stubble.
Continuity mistake: When Palmer comes home and finds the dead American agent on the floor in his flat, the dead agent's eyes and mouth are both wide open. There is a cut to Palmer standing in a door-way, then a cut back to the dead agent, whose eyes are now half-closed and his mouth completely closed.
Other mistake: In the Dr Radcliffe lecture scene, Harry removes his glasses to clean them revealing his poor eyesight. But in the final escape scenes when he determines and shoots the traitor, he is not wearing glasses.