Political debates over Britain’s independent nuclear deterrent offer many causes for depression. One, of course, is the fear of nuclear apocalypse. This, for all its science-fiction improbability, lurks underneath all discussions of the most devastating technology ever conceived of by our species. But a second cause for depression is how magnificently rubbish these nuclear debates generally are.

This is an issue of the utmost importance, central to our nation’s security and – perhaps – the ultimate survival of humanity. But instead of serious, informed and evolving debates, we get posturing jousts masquerading as disagreements of strategic substance. Both those demanding unilateral disarmament and those calling for the full replacement of Trident rely on confident but evidence-less pronouncements about the threats Britain faces, and bald assertions that their opponents are out of touch with both reality and morality.

Labour’s discussions – in the leadership election and since Jeremy Corbyn’s victory – are especially limited and divisive. Labour may have decided against a formal debate at its summer conference, but the underlying contest endures. Corbyn flagged Trident in his conference speech. Shadow cabinet ministers have been staking out positions since his election. And all MPs will need to vote on the issue in parliament next summer.

So what’s truly bizarre is that all these manoeuvres and discussions seem to occur in splendid isolation from any consideration of options other than full replacement of Trident (or, more accurately, the Vanguard-class submarines that launch the Trident missiles) or complete disarmament.

None of Corbyn’s rivals in the leadership campaign tried to balance the real security imperatives with the party’s obvious antipathy towards nuclear weapons by carving out an alternative. And they completely missed a trick, since there is no lack of options here.

Yes, some possibilities have been exposed as non-starters: we can’t just carry on using the existing Vanguard-class submarines indefinitely, and designing nuclear-tipped cruise missiles to be fired from the UK’s newer Astute-class attack submarines wouldn’t save money. But a briefing by the Royal United Services Institute identified four more serious alternatives, while CentreForum, a think tank, proposes shifting to an aircraft based nuclear deterrent, although whether this would save money is disputed.

The Liberal Democrats have aligned themselves to the policy of ending the current 24 hour, 365 days a year deployment of a submarine on patrol – the “continuous at-sea deterrent” or CASD – and building two rather than four new submarines. If imagination in this area is really beyond Labour, they could simply steal this policy. Britain could also, building on a recent increase in Anglo-French defence cooperation, push for a system in which France and Britain jointly provide a CASD, rather than duplicating each other’s efforts (and costs) as they do at present.

Once such alternatives are brought into view, the extreme options of full replacement or unilateral disarmament become seriously unattractive. It is not at all clear that the £20-30bn initial cost of full replacement, plus £1.5bn costs per year thereafter, is a sound use of our national resources. The likelihood of a nuclear stand-off with another state in the short term is vanishingly small. Alarmists like to point to the aggressive moves of Putin’s Russia, or the mounting naval tensions between China and its neighbours. But there is no evidence that anyone is interested in nuclearising these hotspots. These have been profoundly 21st-century manoeuvres, exploiting the ambiguities of cross-border fait accompli deployments of military assets or support to non-state proxies. The world might change, of course, but that will not happen overnight, leaving time for Britain to adapt.

Contrary to Conservative bluster, this is not just the opinion of national-security-illiterate-lefties. As the Royal United Services Institute’s briefing highlights, the government’s own 2010 Strategic Defence and Security Review “is based on the assumption that a significant threat of attack on the UK homeland by other states will not re-emerge without an extended period of strategic warning.”

There is thus a direct contradiction between the government’s rationale for full nuclear replacement and its organising assumptions for the rest of its defence policy. Many members of the RUSI itself – hardly a refuge of the loony left – oppose full replacement, as do a wide range of international security experts and senior military officers. Maybe the costs would be worth it if we could just conjure money out of nowhere – some ‘nuclear quantitative easing’, perhaps. But we can’t. To waste billions on a full replacement of Trident is to take money away from other defence and social priorities, threatening members of the armed forces and the British people at large.

But unilateral complete disarmament is just as dangerous, for four reasons. First, whilst nuclear crises and stand-offs are close to unthinkable in the short-term, they could return in the future, as American hegemony declines and nuclear technology spreads amongst middle powers like Iran, North Korea or Pakistan. These countries won’t suddenly decide to try and wipe Britain off the map. But when one state in a dispute has nuclear weapons and the other does not, the nuclear power can always threaten escalation to a point where its opponent has no defence. That could be used to elicit considerable concessions out of Britain on our vital interests.

Imagine how different the Falklands War might have been if the Argentine military junta had possessed nuclear weapons and the UK had not. Alternatively, a really ghastly regime, perhaps an ISIS-like entity that gains statehood and then acquires nuclear weapons by elicit trade, might be more prone to launch them directly against the UK or our allies if the certainty of deterrent is not present. Now, these scenarios are certainly unlikely. But they are far from unthinkable, and cannot just be wished away. Abandoning nuclear weapons creates a serious lag time to redevelop them if the world security environment worsens. And such redevelopment would be seen internationally as a far more threatening move than merely renewing an existing deterrent.

Second, full disarmament puts Britain in a position of complete security dependence on America. That’s concerning, because we cannot be blasé in assuming that America will always be willing to risk its own citizens lives by credibly promising to retaliate against any aggressor on Britain. Moreover, such dependence could erode Britain’s ability to maintain a foreign policy autonomous from America’s. Might a hard-line future US president use such dependence to pressure the UK into supporting foreign policies we should really keep our distance from? Again, such scenarios are unlikely, but eminently possible.

Third, if one is willing to disarm, one may as well use that willingness to elicit some multilateral disarmament measures from other states, rather than going alone and wasting the opportunity. Such multilateral disarmament might be critical in a future world with more nuclear players. Now, there is probably a grain of truth to the thought that if Britain engaged in nuclear disarmament this would give us some persuasive capital to try and pressure others to do the same. But such positive feeling is never going to be more powerful than an actual multilateral agreement in getting a threatening state to reciprocally disarm.

And that brings us to the fourth reason. As Ian Leslie pointed out in a recent essay in the New Statesman, most people would love to see a world free from nuclear weapons, but disarmament – even in the complete fantasy world in which it is mirrored by all other world powers – wouldn’t create this in a meaningful way. “Knowledge,” Leslie reminds us “once acquired, cannot be unlearnt. Even if all the nuclear powers got together and agreed to dispose of their nuclear arsenals, they would still be nuclear powers, just latent ones”. And that creates a considerably more unstable and tense environment than one with mutual deterrents.

This isn’t to suggest that we can’t get pretty close to a world free from the risk of nuclear conflict. But that will be achieved by a massive, multilateral effort to internationalise the ownership of nuclear technology and a dense regulatory framework for all global production of such technology, with deviations rigorously and universally enforced. There is no roadmap whatsoever from British unilateral disarmament to such a world. Indeed, for the reason mentioned above, unilateral disarmament would take away one of our only bargaining chips in pushing for it.

So, given the severe problems with both the full replacement and complete disarmament options, why is Labour eschewing a serious debate over the alternatives?

Conservative policy is highly vulnerable here. The basic issue is whether the UK really needs to maintains the constant submarine patrols required for continuous at-sea deterrence. Most alternatives in some way back down from CASD, envisaging a force that is CASD-capable but not always active, or a force incapable of CASD that would instead be deployed for long but finite periods when the risk of crisis rises.

The Conservatives’ rejection of all such possibilities rests on muddled thinking and empty assertions. All the scenarios where we could really need nuclear weapons are – as the government’s strategic review states – pretty unforeseeable in the short to medium term. So our nuclear deterrent is doing close to nothing to protect UK national security in the here and now. As noted, new threats could emerge in the future. But CASD is built on a logic of protecting oneself against a state with whom Britain is in a permanent state of genuine nuclear tension – like the Soviet Union of the 1960s. It is hugely unlikely that the world will return to that state of affairs. And if it did, Britain could adapt by building additional submarines.

The much more plausible, though still unlikely, future scenario is one where Britain occasionally finds itself in limited crises with other nuclear armed states, not permanent stand-offs. Limited crises do not require the extravagant over-the-top vigilance of 365 day a year patrols. Conservatives counter by arguing that without a continuous deterrent, Britain would have to dangerously escalate a situation by launching a submarine during a crisis. This is not a convincing claim. Increasing one’s defensive readiness is always part and parcel of a nation’s response to threats. Throughout Cold War crises both superpowers made numerous and repeated moves of escalation (ever heard of DEFCON?) often in a very calculated manner. These were not insuperable obstacles to crisis management. Moreover, a non-continuous at-sea deterrent would be activated for lengthy periods as the danger rises, not at the height of a crisis.

So what should Britain’s defence priority be here? First, to possess as limited and low-cost a nuclear deterrent as possible, for the exceptionally unlikely scenarios when it could be needed in the medium-term. Second, to maintain strategic flexibility in response to a changing security environment – which could easily reduce the need for nuclear weapons as well as increase it – by retaining the capacity to expand or contract our nuclear assets in future.

Replacement on the scale the Conservatives are proposing is totally unnecessary for these objectives and damages Britain’s national security by taking resources away from genuine needs. The wars in Afghanistan and Iraq exposed basic failures of supply for British troops in armour and aerial support. And we are currently building two advanced new aircraft carriers at a cost of over £6bn, but cannot afford the complements of aircraft they need when launched.

A welter of new security demands also need urgent investment: notably in cyber-security, counter-terrorism and unmanned intelligence and combat systems. Our priorities for defence spending should be properly protecting the front line men and women of our armed forces, and empowering Britain’s capacity to respond to complex 21st Century crises around the world, not speculatively gambling on unnecessary nuclear contingencies.

This is where Labour should position themselves. Because there’s also a broader Conservative vulnerability at stake. On the one hand, the Conservatives tell the public that there is simply no alternative whatsoever to severe benefit cuts for the disabled, elimination of tax credits for the poorest, and financial crisis in the NHS. But on the other, they press ahead with the sorts of spending the Tories approve of – a massive defence project with a spurious aura of toughness on national security.

A more moderate plan could save around £5-8bn on the replacement programme itself, and significantly reduce longer-term running costs. Labour should funnel much of that into the genuinely necessary defence spending mentioned above, since protecting our soldiers shouldn't be a ‘right wing’ concern. But they could also take a slice of the savings to help fund economic alternatives to the approach represented by Osborne’s regressive last budget.

All of that would be better for Labour, better for British security, and better for the British people. Seems worth a debate, at least.

Jonathan Leader Maynard is a lecturer in International Relations at the University of Oxford, and a Research Associate of the Oxford Institute for Ethics, Law and Armed Conflict. His research specialises on international security, ideology, and political violence.