First Secretary Eoin MacWhite informed all missions of Aiken’s concerns that U.S. nuclear information agreements with selected NATO partners could impede efforts to prevent the spread of nuclear weapons. He was nonetheless reticent when it came to lodging a formal protest, having been advised by Eoin MacWhite that a strong denunciation would be counterproductive. From MacWhite’s reading no actual nuclear information would be transferred to Allied personnel after all. The agreements related specifically to information necessary for the training of Allied personnel in the employment of U.S. atomic weapons in their hosts’ territories, so Aiken recoiled from further diplomatic protests. He appreciated the need to maintain some nuance on nuclear sharing as he pursued an East-West consensus. 

The strength of NATO's feelings in favor of enhanced alliance nuclear defense and cooperation in the aftermath of the Sputnik shock was well known. The Irish were aware of the Eastern bloc’s objections to NATO nuclear sharing as a dangerous precedent that strengthened NATO’s political and security position. Moscow was especially exercised by any prospect of West German access to nuclear weapons as part of the normalization of German rearmament and progress toward reunification. Moscow opposed any semblance of Bonn’s finger on the nuclear trigger, or its troops gaining proficiency with nuclear weaponry. 

Aiken’s landmark address to the plenary of the UN General Assembly on 19 September 1958 launched his non-proliferation campaign. It is the first time he publicly identified stopping the spread of nuclear weapons as a concrete step in the collective interest to unblock the disarmament impasse, preventing a runaway arms race among the powers of the Earth. It was clearly framed as part of his wider campaign for global governance based on the rule of law rather than the threat of force. For Aiken, the challenge was stabilizing the arms race and generating trust to construct a world order based on justice and law – “to preserve a Pax Atomica while we build a Pax Mundi.” This speech was a critical departure. The widespread positive reception encouraged Aiken, persuading him to draft a formal resolution.

Nonproliferation talks entered their decisive phase after the submission of a joint U.S.-Soviet draft to the ENDC on February 21, 1967. One week later, High-Commissioner of the French Commissariat à l’énergie atomique, Francis Perrin, assessed France’s options. It was not “by accident,” he noted, the original five UN Security Council permanent members—the United States, the United Kingdom, France, the Soviet Union, and China—were in line for nuclear-club membership: “…they are the same profound reasons, of a geographical, demographic or other nature, which led to the choice [in 1945] … of the countries with special responsibilities in the maintenance of world peace.” After noting how advances in “India, Israel, Japan, Sweden, and also West Germany” portended the further spread of nuclear weapons—and acknowledging France had itself sought help with its weapon program—Perrin pondered whether proliferation might hasten nuclear disarmament by convincing the superpowers of its merits. In the end, however, fear of a “large and hostile” nuclear-armed PRC made him pessimistic. While he did not advise signing the NPT, it would be “very important” for France to affirm publicly, if unilaterally, “its constant policy since 1958 … not to cede any atomic weapon or any atomic explosive device to a country which does not possess it, and not to help any such country to manufacture them.” He dismissed internal opposition toward the NPT as defensive—"an a posteriori justification of the French decision to constitute an atomic armament." More significant was the likelihood West Germany would gain its own atomic arsenal, jeopardizing France’s “dominant political position among the Europe of the Six” members of the European Communities and reviving Cold War tensions in Europe. He finished with an eye-opening analysis of how the Kosygin proposal for nuclear-weapon states to extend negative security guarantees to non-nuclear-weapon states’ signatory to the NPT would not impede the use of French nuclear armaments against a West German blitzkrieg backed by the United States.

Subsequent to De Gaulle's November 1967 veto of Wilson's EEC application, senior British ministers still saw the European question as having considerable importance. Shortly before his departure from the role of Foreign Secretary, George Brown reported to the Defence and Oversea Policy Committee that the ructions over Article 3 of the NPT would be "particularly awkward for us as potential members of EURATOM and the E.E.C." De Gaulle's second "Non!" only served to postpone Britain's membership of the EEC, as Edward Heath's Conservative government successfully campaigned for accession, which took place in 1973.

Two "Notes for the Record" from March 1, 1967, describe the vigorous discussions between senior UK government figures, including Harold Wilson, Foreign Secretary George Brown, Minister of State for Foreign and Commonwealth Affairs Lord Chalfont, and chief scientific adviser to the government Solly Zuckerman. Brown argued that "our posture on the matter should be distinctively European rather than one of supporting the United States against other European countries." Wilson was even more explicit, stating that "our approach should be that of a European power discussing the matter with European partners and not seeking to fight American battles." Wilson was keen to let Washington take the lead so that his government might avoid upsetting the French, as had happened with the debates over De Gaulle's 1966 withdrawal from the NATO command structure.