By William Walker

International nuclear relations were already in crisis before Russia’s assault on the Ukraine. Since the late 1990s, arms control treaties have been abandoned and commitments to nuclear disarmament dishonoured. Instead, nuclear arsenals are being expanded and modernised, encouraged by the return of hegemonic rivalry, China now being involved.

Most ominously, technological change, involving cyber warfare, automation, hypersonic missiles and much else, has raised serious questions about the future safety and reliability of nuclear deterrence, as has the emergence of untrustworthy and unprincipled leaders with fingers on the button and contemptuous of international law. Although exceptionally grave, Russia’s threat to use nuclear weapons to protect itself in its war of aggression against a non-nuclear weapon state has been the latest in a string of developments undermining the rule-based nuclear order.

The result has been deep unease about the direction of travel. The bolstering of nuclear deterrence has become the immediate priority for nuclear-armed states and alliances. At the same time, there is realisation that global disorder and catastrophe lie ahead if the nuclear juggernaut is not reined in. Their avoidance demands a reinvigorated engagement with nuclear arms control and disarmament.

Scotland will probably find itself stepping into a febrile, polarised and dangerous political and strategic environment if it gains independence through a legally recognized referendum in the next few years. The United States and European allies can be expected to join the UK’s remnant in pressing for the submarine fleet’s stay in the Clyde. The rewards for Scotland’s making concessions would be substantial, as would be the costs of insistence on the nuclear bases’ early closure. Although concessions are likely, the bases’ permanence in the Clyde would be impossible for an independent Scotland to accept. Besides the traditional objections, consenting to the UK nuclear force’s occupation, in effect, of a chunk of Scotland’s prime sovereign territory (land, loch and sea) in perpetuity would be a step too far. That a sovereign Scottish state could have little or no say over the weapons’ deployment and use in war would also be hard to live with.

Nor would the nuclear navy and government in London relish the prospect of running the nuclear submarines out of an independent Scotland. Authority retained under devolution would go. Various political, logistical, safety, planning and policing issues would need constant and willing attention by the two governments. There is also no precedent for a nuclear weapon state’s operation of its entire deterrent out a legally constituted non-nuclear weapon state, which Scotland would become after joining the Nuclear Non-Proliferation Treaty, as it must.

From Day 1, the Ministry of Defence in Whitehall would be wondering whether Trident’s operation out of Scotland could be sustained, whether alternatives should be sought, and whether the security benefits and opportunity costs of an increasingly vulnerable system, with its few lumbering submarines, would remain worthwhile given the march of technology. Ultimately, Edinburgh and London’s goals might not be dissimilar. Even if Scotland conceded to the current system’s lengthy stay, perhaps into the 2040s, the Holyrood and Westminster Parliaments are unlikely to agree on embarking on a second renewal involving Faslane and Coulport. Trident’s first renewal, still incomplete, will have taken three or more decades to achieve. The replacement clock would again begin ticking in the 2030s.

Come what may, Edinburgh and London would be compelled to forge an agreement on the nuclear future after a yes vote. Success would depend on mutual acceptance of two guiding assumptions: Trident’s operation out of the Clyde required extension; and the extension could not be indefinite. Seeking a compromise along these lines would seem eminently reasonable abroad. It would be hard for any government, including the French and American, to reject it out of hand.

This implies two linked sets of agreement – one on continuation, the other on phase-out –the first and possibly the second taking the form of an international treaty compliant with international law and procedure. Each would be complex, the timing of phase-out and its initiation being especially contentious. Since details might take years to work out, an initial framework agreement would probably be required.

The treaty on continuation would need to cover the terms and conditions of leasing the bases (surely the only option), Scotland’s rights of consultation and decision, management and protection of waterways, transport of warheads, and policing and intelligence gathering among many things. The largely informal arrangements under which US airborne nuclear weapons are based in Europe and the Far East, and NATO’s nuclear sharing arrangements whereby weapons may be carried on a host nation’s aircraft (their activation still under US control), could not apply where submarines are involved.

Issues addressed in the agreement on phase-out would include the preparation and timing of withdrawal of the nuclear force, the bases’ dismantling, decommissioning and decontamination, and the allocation of tasks and division of costs. Even if London accepted the principle of phase-out, setting a time-frame would be inherently problematic since it has conducted no assessment of alternative sites other than with the broadest of brushes (Cornwall and the US have been mentioned). Costs and political feasibility are difficult to judge in advance. An exploratory period would probably have to precede full negotiation of an agreement on phase-out. Somehow, an agreement would need to allow some flexibility whilst still being binding on the parties.

These agreements would be necessary but tough to achieve. Difficulties would be compounded if the Scottish and UK Governments entered negotiations without prior examination of the issues and how problems might be resolved. Brexit has displayed the perils of not squaring with the public, of embedding red lines, and of being grossly unprepared for what follows.

After a yes vote in a second referendum, Trident’s fate would become central to the establishing of cooperative relations between Scotland, the rest of the UK, and the wider world. Reaching a settlement in this vital field would be in everyone’s interest. The Scottish and UK governments both bear a responsibility for not going blind and bound into the negotiations, and for being open to compromise come the day.

William Walker, is Emeritus Professor, School of International Relations, University of St Andrews