Who is MacNamee from The Innocent and what is their importance?

MacNamee is the British secret service agent assigned to the warehouse tunnel project. He is described as a friendly but guarded man, and he is eager to equal if not better the success of the Americans on the project. His decision to enlist Marnham's aid in spying on the Americans, thus, increases Marnham's security status and defines both Marnham's journey of transformation, as well as the resolution of the espionage plot.