London, UK - At an unknown location somewhere deep beneath the world's oceans, a British submarine sits primed to launch up to 40 nuclear warheads with a collective destructive power almost 300 times greater than the atomic bomb dropped on Hiroshima in 1945.
Since the late 1960s Britain's nuclear deterrent strategy has required that at least one of the Royal Navy's four-strong fleet of Vanguard submarines be operational and fully armed at all times, providing, according to the navy's website, a "round-the-clock insurance policy”.
Only a British prime minister has the authority to order a nuclear attack.
But, in the event that a submarine commander loses radio contact and suspects his homeland has been wiped off the map, orders contained in an onboard safe reputedly offer a choice to either "let them have it"or "sail to New Zealand if it's still there”, according to documents unearthed by Peter Hennessy, a veteran historian of British state secrets.
Conceived in response to the perceived threat of a surprise Soviet assault on western Europe, Britain's deterrent remains a classic throwback to the nuclear brinkmanship of the Cold War.
Yet, two decades after the Soviet Union's collapse, the UK government this week took a big step towards replacing its current submarine-launched Trident missile system with a like-for-like successor that would take to the seas by 2028.
"Our nuclear deterrent is the ultimate safeguard of our national security. We have made a clear commitment to maintain that deterrent," said Philip Hammond, the British defence minister, announcing an additional $565m in spending - on top of $4.8bn already committed to the project - for design work on a next-generation replacement for the Vanguard fleet.
Hammond's announcement immediately stoked divisions between his own ruling Conservative Party and their Liberal Democrat coalition partners by seeming to fly in the face of government policy postponing the final decision on a replacement until 2016, pending the results of a Liberal Democrat-led study into possible alternatives.
"Defence chiefs are under concerted political pressure to cut spending, even with the armed forces already overstretched by the war in Afghanistan and other commitments."
Nick Clegg, the deputy prime minister and leader of the Liberal Democrats, responded by questioning the wisdom of "spending billions and billions of pounds on a nuclear missile system designed with the sole strategic purpose of flattening Moscow at the press of a button”.
Hammond also drew the ire of nationalists in Scotland by presuming the continuing presence of a British nuclear arsenal at the Faslane naval base on the country's west coast beyond a 2014 referendum on independence.
With the Scottish National Party committed to banning nuclear weapons in the event of it winning power after a split from London, a parliamentary committee warned this week that the UK's deterrent could be "unilaterally disarmed" within days of secession.
Yet, even disregarding the immediate political fallout, many defence experts now argue that a replacement deterrent is something that the UK neither needs nor can afford.
Defence chiefs are under concerted political pressure to cut spending, even with the armed forces already overstretched by the war in Afghanistan and other commitments.
Limited defence resources
Meanwhile, the 2005 London bombings and similar attacks against western targets seemed to point to a new paradigm in which the main security threat comes from nebulous networks rather than rival nation states, rendering traditional deterrent strategy as redundant as the cavalry charge.
"No one's got a crystal ball. You can never categorically rule out fanciful scenarios of a revanchist Russian state and that kind of 'Cold War redux' scenario," said Nick Ritchie, a lecturer in international security at the University of York.
"But when one looks at the strategic security environment we're in, it's very difficult to make the case that if we didn't have nuclear weapons now we would survey the scene, and make a judgment that we categorically must have them.”
While the government has estimated the cost of a replacement system at about $32bn, critics argue that the final bill could be upwards of five times that amount.
"In the land of serious policy planners it's very hard to argue for us remaining in the nuclear weapons business," added Ritchie. "You have to ask, is this the best way to spend limited defence resources?”
"There is a strong sense that for us to be a nuclear weapons state is almost part of who we are on the international stage."
-Nick Ritchie, Lecturer in international security at the University of York
Others argue that the money would be better diverted instead to bolstering public services struggling under the weight of the government's austerity measures. "Obscene that government plans to spend hundreds of millions on nukes, while slashing welfare & benefits," tweeted Caroline Lucas, a Green Party member of parliament.
Yet the role of Britain's nuclear deterrent is linked to the political and military establishment's perception of the country's place at the world's top table. It's a matter of pride for some that the UK is one of five recognised nuclear-armed states in the Nuclear Non-Proliferation Treaty along with four other permanent members of the UN Security Council: the US, Russia, China and France.
Returning from a bruising encounter with the US secretary of state in 1946, and perhaps feeling acutely conscious of Britain's fading status as a world power, Ernest Bevin, the British foreign minister, declared that the UK had to have the bomb at any cost, adding: "We've got to have the bloody union jack on top if it.”
The same sentiment can be perceived 60 years later in a passage in Tony Blair's memoirs in which the then-prime minister admitted that he could clearly see the "common sense and practical argument" against renewing Trident even as his government laid out plans to upgrade the system in 2006. "In the final analysis I thought giving it up too big a downgrading of our status as a nation," he concluded.
"There is a strong sense that for us to be a nuclear weapons state is almost part of who we are on the international stage," said Ritchie. "That's not a sentiment that's held by the British public. But certainly in the upper echelons of the security and defence establishment I would say there is a feeling that if we were to relinquish a nuclear capability we would somehow not be Britain anymore.”
Dominic Sandbrook, author of a series of histories of Britain since the 1950s and presenter of a forthcoming television series on the Cold War, agreed that the UK's possession of nuclear weapons had long been "more a matter of national virility than national security”. He pointed out, however, that the Trident system and its predecessors' dependence on US technology, including the missiles themselves, belied the idea of an entirely independent British deterrent.
There had been broad public support for the country's possession of nuclear weapons throughout the Cold War, he said. When the Labour Party adopted a policy of unilateral disarmament during its 1983 election campaign, it was promptly trounced at the polls by Margaret Thatcher's Conservatives and its manifesto subsequently derided as the "longest suicide note in history”.
"Public opinion then was much more hawkish on defence, partly because people had been persuaded of the Cold War case," said Sandbrook. "And, by and large, the relatively uninformed voter saw the possession of nuclear weapons as a sign that you're a big power. And the third thing is that the average British punter didn't care that much about the issue.
They didn't think about it. It was just part of the wallpaper of life.”
But some now detect a significant shift in public attitudes - and a political opportunity for a Labour Party bold enough in opposition to shatter the cross-party consensus on the need for a UK deterrent and look once again at the case for disarmament.
Nick Ritchie said that polls canvassing public opinion on replacing Trident had swung from about 60-40 in favour in 2006 to about 60-40 against more recently. When framed as a straight choice between warheads and missiles or extra nurses and more affordable homes, opinion swings even more sharply in favour of giving up the weapons.
Kate Hudson, the general secretary of the Campaign for Nuclear Disarmament (CND), said that opinion polls showed a majority of the British public opposed replacing Trident and said proposals to spend "ludicrous sums" on a new system at a time of "acute economic hardship" had served to reinforce opposition.
"Scrapping Trident is a vote-winner waiting to be seized by a party with the initiative to see beyond the dogma of nuclear deterrence," said Hudson. "Labour must be bold in rejecting entirely a weapons system which serves no purpose but to threaten civilian lives internationally and destroy public services domestically.”
Sandbrook, meanwhile, sees irony in the continuing debate over the future of Britain's nuclear deterrent even as other vestiges of the country's Cold War military defences, such as the secret bunkers to which key workers would have retreated in the event of a Soviet attack, have been consigned to the past.
"The Cold War infrastructure has become part of our national heritage, part of our history," he said. "It's extraordinary at the very time we are converting these sites into museums that the very idea of our need for these weapons has not become a museum piece in itself.”