While the budget deficit was being discussed, Nick Clegg proposed that around 100 billion could be saved by not renewing Trident, a "relic" of the Cold War. One could almost feel the reverberations caused by millions of Britons nodding assent.
Clegg's intervention had huge symbolic importance because it suggested that he is something genuinely new, while the Tories and Labour are mired in the distorted logic of the Cold War. Gordon Brown and David Cameron visibly stumbled trying to defend a hugely expensive, essentially redundant, weapons system. If they had shown up to the debate in flared trousers, polyester shirts and shoulder-length hair, they could not have looked more old-fashioned.
The argument, of course, is not Clegg's alone. Alex Salmond has also railed against the way the "London parties" want to cut social services, instead of cutting Trident. Since 100bn is a figure that commands attention, both party leaders have derived considerable benefit from it.
Unfortunately, the matter is not as simple as Clegg and Salmond suggest.
Clegg will undoubtedly be in for a grilling during today's second debate, on Europe and foreign affairs because, frankly, the 100bn figure is as shaky as a two-legged stool. A 2006 Defence White Paper put the figure more accurately at 65bn over 30 years. Clegg and Salmond appear to have added together worst case scenario estimates for the cost of four submarines (14bn), thrown in 3bn for refurbishing warheads, another 3bn for infrastructure costs, and then added in running costs of 1.5bn/year, multiplied by 50 years, yielding a grand total of 95bn.
Scrapping Trident won't produce an instant saving of 100bn that can be neatly subtracted from the national debt. The upfront costs from 2012 to the end of the decade should not exceed 1bn per year – in other words, less than what some analysts calculate will be the weekly interest payment on Britain's massive debt.
So, should Clegg and Salmond apologise for trying to pull the wool over our eyes? Yes and no. Their guilt lies only in buttressing a basically sound idea with specious figures.
Scrapping Trident makes good sense but, as Clegg undoubtedly understands, trying to sell the plan on practical (as opposed to strictly financial) grounds raises all those tendentious arguments about nuclear disarmament that poisoned politics in the 1980s. Far better to talk about money than to raise the spectre of Michael Foot and unilateralism.
Foot aside, Britain's independent nuclear deterrent was a flimsy notion back in the 1980s and is an entirely spurious one now. In that sense, Clegg is admirably modern, Brown and Cameron hopelessly old-fashioned.
Scrapping Trident addresses a problem that plagues us now, instead of obsessing on a problem from the past. While an extra 1bn per year will not cure the national debt, it will buy a lot of armoured personnel carriers and body armour for British soldiers.
The irony of today is that Britain maintains a hugely expensive nuclear deterrent, but does not actually have any nuclear-equipped enemies to deter. It seems rather silly that our sailors cruise the ocean depths in expensive submarines listening to whales sing, while our soldiers die for lack of equipment in Afghanistan.
That was essentially the argument made by four generals who yesterday broke ranks with the military establishment by arguing that Trident should be scrapped. In a letter to The Times, Field Marshal Lord Bramall, General Lord Ramsbotham, General Sir Hugh Beach and Major-General Patrick Cordingley contend that money spent on Trident could be better used on Britain's actual defence needs, namely frontline troops and counter-terrorism. They maintain that renewing Trident flies in the face of President Obama's pledge to work toward total nuclear disarmament.
In contrast, Cameron and Brown argue that Britain's independent nuclear weapons remain essential as a deterrent to Iran and North Korea. That's an even bigger sham than Clegg's magic numbers. Iran and North Korea are a long way from developing a genuine nuclear capacity, which means not just weapons, but the ability to deliver them. In any case, neither Iran nor North Korea is actually an enemy of the UK; they are enemies of the US. We have to ask what possible motivation they would have for using their precious weapons to destroy Milton Keynes, instead of, say, New York.
Issues of this sort do not complicate elections in Germany or Spain. The Dutch do not lay awake at night worrying about an Iranian bomb, or, for that matter, a Russian or Chinese one. The reason our European friends don't worry is because they live in non-nuclear states. In other words, nuclear weapons, instead of addressing vulnerability, in fact makes a country more vulnerable. That was certainly the case during the Cold War.
The British nuclear deterrent was never really about deterrence. That function was provided by the US , and still is. The real reason was status – in other words, a Bomb would supposedly allow her to strut on the international stage.
Ernest Bevin saw it as an instant solution to postwar feelings of inferiority. "We've got to have this thing over here whatever the cost," he shouted in 1946. "We've got to have the bloody Union Jack on top of it."
Churchill likewise believed that the Bomb allowed Britain "to dine at the top table". Every British prime minister since that time has echoed that.
Yet what benefit has Britain actually derived? It is difficult to discern an advantage, especially since her non- nuclear competitors have done rather well over the last 60 years.
The great tragedy of the current debate is that it is likely to get bogged down in rancour over the legitimacy of Clegg's figures. The much more fundamental matter relating to the logic of a nuclear Britain will probably get pushed to the margins. Yet long after the debt question is solved, the Bomb question will fester.
Gerard DeGroot is a professor of modern history at the University of St Andrews.