Winston Churchill, as usual, gave the policy a floridly eloquent gloss. Britain, he said, almost 50 years ago to the day, must reach that happy condition "where safety will be the sturdy child of terror, and survival the twin brother of annihilation". He was talking about mutually assured destruction, or MAD - the theory of nuclear deterrence that dominated the second half of the 20th century and, uncountable billions of dollars later, kept us supposedly safe from obliteration. If our enemy had a bomb and we had a bomb, then neither of us could use it on the other because we'd both be dead in an instant.  And, at least in a negative way, that seemed to work, because the only bombs anyone dropped - on Hiroshima and Nagasaki - were Uncle Sam's message to non-nuclear Japan. MAD was salvation. MAD was security. MAD was the way of life most of us grew up with, the prevailing logic of uneasy peace. So whatever became of our mad, mad world?  It isn't that such deterrence is a busted flush. It allegedly brings realism to Indo-Pakistan relations and keeps Russia and China sweet. Many more billions of dollars have been spent on refining it since Ronald Reagan dreamed his "evil empire" dreams and decided that his own version of Star Wars could shrug away the chance of a sneak attack. But now a strange silence reigns.  Read George Bush's state of the union address from beginning to end and none of the grand old tunes are there; indeed, just the reverse. We had "outposts of tyranny" - and Iran "as the world's primary state sponsor of terror". We had that Condoleezza riff on the globe's "most loathed regime". We heard, yet again, that "Tehran cannot be allowed to develop nuclear weapons". We heard nothing about our leaders' ancestral faith in mutual assurance. It is surely worth wondering why.  The theory, after all, was never disproved. It appeared, in a flurry of spending, to dispose of the evil empire. It worked between dictatorships and democracies, between Khrushchev and Kennedy. It seemingly works for Islamabad. Why, then, so much sound and fury over Iran, so many threats set aside for the "time being" only? Would a Tehran sandwiched between nuclear Pakistan and nuclear Israel, with nuclear Russia to the north and nuclear America everywhere in the skies above, really pose quite the menace Bush pretends?  Of course, it's cheery when countries which could make a bomb renounce that opportunity. Fewer bombs clearly means less risk of accident (or illicit trafficking). Yet sometimes the hysteria involved in prospective proliferation becomes absurd. A bomb of your own can be hugely popular on the streets, as Pakistan and India demonstrate. But it doesn't change anything very substantive. The subcontinent has fought itself into a cul de sac anyway.  No, the prevailing theory of nuclear deterrence today is far different. It sits snugly alongside George W's lectures on democracy rampant. It says that the only real superpower alone can be trusted to upgrade and hone its nuclear arsenal; that true safety means leaving everything to the White House.  But why on earth should such arguments run in countries like Iran, which have no   reason to hail American hegemony? Iran has nuclear enemies all around, as we've seen. Iran may well hunger after the respect now accorded to Pakistan. In theory - old theory - a Tehran bomb would only complete the regional balancing act. In theory - old theory - it would have stopped Saddam launching his hideous war. What's so worrying here?  There's an answer to that, naturally; a Tom Clancy-style spiel featuring terror groups, greedy scientists, berserk mullahs and the rest (basically cold war porridge re-heated for a new audience). Yet, in truth, it's a thin little theme. Is civil nuclear power fading from use? To the contrary, nuclear power is a continuing fact of 21st-century life that many poorer nations in search of development feel obliged to fund and acknowledge.  In sum, the current international block on nuclear proliferation isn't going to endure. It didn't stop Islamabad or Delhi. It won't, over time, stop central Asian republics from growing uneasy in their nuclear isolation, ringed by bomb-toting countries - or Damascus and Tehran from feeling permanently threatened by Israel's bomb.  The critical difficulty, of course, is perspective. If you even write about Israel's bomb in public, you're deluged with emails saying it can never be given up. Never? Not even in the tranquil Middle East of Condoleezza Rice's present imaginings? No, never. It is the final seal on Israel's security. Why don't you Brits give up your bomb first, those Israelis ask angrily.   And there's the rub. We could do exactly that. Like Germany, Japan, Australia, South Africa, we could walk away. But no British government has the guts. We like to be part of this club of safety's sturdy children. It gives us a certain muzzy status.  We don't want to lose our costly comfort blanket in an uncertain world. But nor do we want to ponder the future of the blanket industry. Thinking about such things makes us oddly uneasy. Better to go through imbecile motions - threatening Iran's Shias, say, just as Iraq's Shias sweep to power over the border - than contemplate steps to a bomb-free world. Better to demonise Islam further by shivering over an Islamic bomb.  In a sense, it's almost reassuring to see Moscow and Washington falling out again this morning: twin brothers of annihilation able to snarl but not think afresh, glad to be mad in their crazy cocoon.