Nuclear disarmament is once again back on the agenda as officials from around the world will gather over the next few weeks at the United Nations Headquarters in New York to review the progress of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).

With eyes turning to US and Russia's stagnation in reducing their large nuclear stockpiles, across the Atlantic, the UK's nuclear weapons system, known as Trident, has become a contested issue in the run up to the general election.

Up for renewal, Trident has divided British politics for decades, and it is likely that whoever is in power following May 7 will have to make tough choices — politically, financially, strategically, and ethically — over the program's future.

Political decisions: possible power struggles and backroom negotiations

The UK's main political parties, the Conservatives and Labour, have pledged to renew Trident, an ocean-based nuclear weapons system. The system is composed of three parts: four aging submarines (where one submarine is on patrol at any time, or "continuous at-sea deterrent"), missiles, and nuclear warheads. The warheads are placed on the Trident II D5 ballistic missiles, and the missiles are maintained and stored under a joint agreement with the US at the nuclear missile submarine base at King's Bay, Georgia. A decision whether to renew the Trident fleet, under the Successor program, is due to be taken in 2016.

In their manifesto, the Conservatives pledged that they would retain the nuclear deterrent and build four costly Successor-class Ballistic Missile Submarines. Labour, who did not explicitly reference Trident in their manifesto, also said that it "remains committed to a minimum, credible, independent nuclear capability, delivered through a continuous at-sea deterrent." This week, Labour's shadow defense secretary Vernon Coaker told the BBC that the party is committed to four submarines, but the renewal of Trident may provoke internal party conflict since, as revealed by the New Statesman, 75 per cent of Labour's parliamentary candidates are against renewing Trident.

If there is no outright majority for the Conservatives or Labour, then there is a likelihood that a coalition with smaller parties could be formed, with, for example, the Liberal Democrats, the Scottish National Party (SNP), or the Green Party. If this was to happen, then the declared leader of the election may have to negotiate with these parties over the future Trident. The Liberal Democrats want to "step down the nuclear ladder," conscious of its commitments to the NPT, and procure fewer submarines. The Green Party would cancel Trident's replacement and decommission existing nuclear forces and facilities, while the SNP would "oppose plans for a new generation of Trident nuclear weapons and seek to build an alliance in the House of Commons against Trident renewal."

There has been some suggestion that the SNP could be a coalition partner for Labour, although there has been mudslinging galore over this potential collaboration. In late March, the leader of the SNP Nicola Sturgeon said: "Under no circumstance would we ever vote for the renewal of Trident or the spending of money on the renewal of Trident." She continued: "In terms of any formal arrangement with Labour, I've made clear and I can't make clearer, Trident is a red line." Days later, Conservative Defense Secretary Michael Fallon called Ed Miliband, the leader of the Labour party, "a man so desperate for power he is ready to barter away our nuclear deterrent in a backroom deal with the SNP." Labour said that Trident was not up for negotiation.

Financial decisions: to invest, or not to invest?

The cost of Trident has repeatedly been called into question, particularly in these austere times where money could be invested in, for example, schools and hospitals. The next political leader would have to justify this expense to the electorate in 2016. According to a recent update from the House of Commons Library, at 2013/14 prices, it is estimated that the Successor programme will cost 17.5 billion-23.4 billion pounds ($26.5bn-$35.4bn), including 12.9-16.4bn pounds for the submarines. If the new submarines come into service, it would take up around 5-6 percent of the defense budget.

The SNP, Green Party, and Campaign for Nuclear Disarmament (CND), however, have estimated that over the course of its lifetime, the nuclear deterrent would cost 100bn pounds, which includes the procurement of the new submarines, the upkeep of the submarines, and decommissioning costs. Yet some argue that this is a small price to pay to keep the country safe.

Speaking to VICE News, Dr. Azeem Ibrahim, lecturer in international security at the University of Chicago and research professor at the US Army War College, said: "Trident's cost is 100bn pounds over a certain number of decades. However, if you look at the actual cost on an annual basis, that's actually a fraction of UK GDP. Many would argue that's a very small price to pay to have the ultimate insurance policy in a very uncertain world."

It has been suggested that the renewal is going to take up a chunk of military spending. According to a recent paper by Professor Malcolm Chalmers of the Royal United Services Institute (RUSI), replacing the submarines is likely to be the "single-largest procurement program of the next decade." The paper indicates that spending on nuclear submarines and other deterrent capabilities is projected to need 40bn pounds from 2014/15 to 2023/24 — 25 per cent of the equipment procurement budget. It is calculated that by the early 2020s, the program is planned to take up a third of that budget.

With such a large amount of money potentially being invested in Trident's renewal, it raises concerns over the spending of other military capabilities. Speaking to VICE News, Paul Ingram, executive director of the British American Security Information Council, said: "The Ministry of Defense cannot afford Trident plus all of its other missions. So there is indeed a direct choice to be made between having a brand spanking new nuclear weapons system that nobody expects to use, or hope is never used, and being a country that has conventional forces that has relevance on the world stage."

Cheaper alternatives to Trident have been proposed, such as reducing the number of submarines from four to three, or even two, abandoning the "continuous at-sea" aspect of Trident as the Liberal Democrats have suggested. Yet if this were to occur, the reduced submarines may be vulnerable to attack. "Theoretically, although very unlikely, there will be a time where all three of submarines will be in the same port. Therefore if you have an adversary, and it wanted to make a preemptive strike on the UK, you would be technically vulnerable to what is called a "counterforce" nuclear strike, which is when an adversary targets your nuclear weapons, so they strike in the hope to eliminate all the capacity you have and you can't retaliate," Timothy Stafford, research analyst at RUSI, told VICE News.

He continued: "The principle of having one on patrol at all time is that every adversary knows that it cannot eliminate all the capacity in the first strike."

Another alternative put forward by Toby Fenwick, a research associate at the CentreForum think tank, proposed that nuclear deterrence could be provided with aircraft instead of submarines, operating from land bases and Royal Navy carriers, saving billions of pounds for the conventional forces.

But using aircraft could increase the UK's nuclear weapons stockpiles, as Dr. Andrew Futter, senior lecturer in international politics at the University of Leicester, explained to VICE News: "You would need to have an awful lot of aircraft carriers or bases in different countries. You need to have a new missile, and possibly a new warhead. There are big problems of creating new missiles, due to Britain's commitments to NPT. It would also possibly mean a larger stockpile of warheads than we have at the moment. Also, airplanes are far more vulnerable, they can be shot down. They're vulnerable to air defenses."

Strategic decisions: the role of the UK's nuclear deterrent on the international stage

Whoever is in power next is likely to face a debate over what kind of "uncertain" threat the UK is facing. An open letter signed by 20 former defense chiefs, urging the next leader not to abandon Trident, stated on Wednesday: "In an uncertain world where some powers are now displaying a worrying faith in nuclear weapons as an instrument of policy and influence, it would be irresponsible folly to abandon Britain's own independent deterrent."

Recently, relations between the west and Russia has been frosty. President Vladimir Putin said he was ready to put the country's nuclear weapons on standby during the Ukraine crisis. And then there was the story of a suspected Russian submarine almost capsizing a UK fishing trawler. As Paul Mason's blog for the Guardian points out, Putin complicates the Trident picture.

But then again, perhaps the more pressing threat is somewhere in the world where nuclear weapons are ineffective, as recognized by former defense secretary Michael Portillo speaking to the Financial Times in 2013: "I think [the UK nuclear arsenal] is completely past its sell-by date," he said. "It is neither independent, nor is it any kind of deterrent because we face enemies like the Taliban and al Qaeda, who cannot be deterred by nuclear weapons."

The extent to which the UK's nuclear deterrent system is independent raises some interesting discussion. It harks back to the 1950s, when the UK and the US signed the Mutual Defense Agreement, establishing a relationship where parties could exchange nuclear expertise and technology, as well as allowing the UK to conduct nuclear testing at US facilities, thus reducing costs. This nuclear relationship has long continued. Currently, the US is helping the UK with some elements of the Successor programme, such as the development of the Common Missile Compartment.

Trident also plays a part in NATO, assigned to the organization since the 1960s as a way to share the burden of defense with the US. Others disagree as to how essential the UK's nuclear weapons system is to NATO. "I don't think it is vital to NATO. If it was, you'd have a lot more countries within NATO that would be nuclear armed," said Pete Wilkinson, director of the Nuclear Information Service. "I don't see why the UK being this fairly small, relatively insignificant offshore island from mainland Europe be the one that has the nuclear weapons? Others are quite happily members of NATO without nuclear weapons. There's no entrance fee for NATO saying that you must have nuclear weapons at all."

But now the US may be keeping a watchful eye over how the Trident renewal plays out, "perhaps as an indicator of military spending," RUSI's Stafford told VICE News.

He continued: "As far as the US is concerned, the UK is a primary partner in Europe, and there are substantial concerns over the UK's level of expenditure and whether it would fall below 2 percent of GDP, the agreed upon NATO threshold."

Recently, US diplomat Samantha Power expressed concern that its European NATO allies are cutting defense military budgets to the extent they are unable to maintain that spending target. According to research by RUSI's Chalmers, the UK is due to fall below the 2 percent threshold in 2016. Furthermore, the head of the US army recently stated that he was concerned about the impact of defense cuts on the UK's armed forces.

Speaking in 2013 to the Financial Times, Steven Pifer, former US ambassador and director of the Brookings Arms Control Initiative, said: "If the UK Trident programme sucks up so much money that the British military is denuded of expeditionary capabilities that are far more likely to be used than nuclear weapons, the US military will not be happy about that."

Ethical decisions: the question of nuclear disarmament

Alongside growing pressures on military spending, the next UK leader would also have to examine the ethical debate surrounding the renewal of Trident, particularly its obligations of nuclear disarmament under NPT. According to BASIC, the UK has no more than 225 nuclear warheads of which 160 are classed as "operationally deployed," and it was decided in 2010 that the total amount of nuclear warheads is to be reduced to 180 by the mid-2020s.

At the peak of the Cold War, the UK had a stockpile of 520 nuclear warheads. "Our Ministry of Defense and political leaders frame the UK as the most progressive of nuclear weapons states," Dr. Nick Ritchie, lecturer in international security at the University of York, told VICE News. But he continued: "There's still this underlying commitment to the necessity of having nuclear weapons in our defense for our security. We see this in the narratives around Trident in the general election. There's a competition between Labour and Conservatives to demonstrate just how committed they are to keep nuclear weapons for the foreseeable future because they're somehow essential and necessary for our security."

According to House of Commons library research, past governments have maintained that the renewal of Trident is compatible with the UK's obligations under the NPT. Yet non-nuclear states party to the Treaty may not look favorably on the UK.

"The perception of good faith efforts by the nuclear weapons states on disarmament, on transparency, [whether that is] on reducing nuclear risks in general, or reducing the number of weapons and delaying modernization decisions — all those things matter," Sharon Squassoni, director of the Proliferation Prevention Program at the Center for Strategic & International Studies, told VICE News.

"And when someone from a non nuclear-weapon state looks at the UK, which says its going to spend 100bn pounds on replacing their nuclear weapons, it is easy to conclude that those nuclear weapons aren't going anywhere soon. So disarmament is not going to happen in the next 50 years, not when you spend 100bn on replacing them."