The Fourth Protocol (1987)

Caine plays a senior British administrator who is part of the intelligence establishment. When his findings offend his superiors he is reassigned to a customs post. While there he finds odd things showing up, which might well be parts of a small nuclear device. A Russian agent has been sent to England with instructions to assemble the device just prior to the British election next to an American Air Base in order to throw the election to Labor and get Britain out of NATO.