Today the nuclear non-proliferation regime is under pressure. We have already seen the emergence of a mixture of further declared and undeclared nuclear powers. And now, two countries - Iran and North Korea, both signatories of the nuclear non-proliferation treaty - remain in open defiance of the international community. Each of them raises the serious prospect of proliferation across their region. Terrorists have declared their willingness to use nuclear material. And we have to make sure that countries can generate electricity from nuclear fuel, while strengthening the safeguards that will stop nuclear materials or nuclear know-how falling into the wrong hands. Those are serious challenges but there is no reason to believe that we cannot rise to them. Despite the recent log-jam, the basic non-proliferation consensus is and has been remarkably resilient. The vast majority of states have not developed nuclear weapons. Far fewer states than was once feared have acquired and retained them. The recognized nuclear weapons states themselves have made significant reductions in their nuclear arsenals. But, as I argued on Monday at a major international conference in Washington, if we want results on nonproliferation, we will need to show much more ambition and action on nuclear disarmament. Those who currently have nuclear weapons have to be serious - and seen to be serious - about a world free of nuclear weapons. The majority of countries - those whose support is vital to the international consensus on non-proliferation - want and expect those states to do more to fulfill our obligations under the NPT. If we do not, potential proliferators will try to use our disagreements to their advantage. And that need to reinvigorate our collective commitment is just as crucial at the regional level. The international community's clear commitment to regional zones free of nuclear weapons, including in the Middle East, is a vital supporting pillar of the non-proliferation regime. NUCLEAR WEAPONS states should certainly be much more open about the disarmament steps they have already taken: the vast cuts in warheads, some 40,000 made by the US and Russia since the end of the Cold War, as well as the cuts that France and the UK have made to our much smaller stocks. But this is not a problem of perception only. The sense of stagnation is real enough. There is a dangerous absence of debate at the highest levels on disarmament and a collective inability thus far to come up with a clear, forward plan. We need both vision - a scenario for a world free of nuclear weapons - and action - progressive steps to reduce warhead numbers and to limit the role of nuclear weapons in security policy. History has shown us how bold vision can lead to bold action. Would William Wilberforce, for example, have achieved half as much if he had set out to "regulate" or "reduce" the slave trade rather than abolish it? I doubt it. So too with nuclear weapons. Believing that the eventual abolition of nuclear weapons is possible can act as a spur for action on disarmament. Believing, at whatever level, that it is not, is the surest path to inaction. TAKING ACTION does not mean setting an unrealistic timetable for the abolition of nuclear weapons. That would require much more than disarmament diplomacy - it would require a much more secure and predictable global political context. Such a context does not exist today. Indeed it is why the UK recently took the decision to retain our ability to have an independent nuclear deterrent beyond the 2020s. But acknowledging that the conditions for abolition do not exist now does not mean resigning ourselves to the idea that we will never reach that point. Nor does it prevent us from taking steps to reduce the number of nuclear weapons and to start thinking about how to get rid of them completely. The UK, for example, has announced a further 20 per cent cut to the number of our operationally available warheads. And we have said that if the conditions were right we would get rid of the rest of them. Globally we will need three steps. Each on its own is a positive move and each gets us further in the direction of a world free of nuclear weapons. First further reductions in warhead numbers, particularly in the world's biggest arsenals. There are still over 20,000 warheads in the world. Almost no-one - politician, military strategist or scientist - thinks that warheads in those numbers are still necessary to guarantee international security. Second pressing on with the Comprehensive Test Ban Treaty and with the Fissile Material Cut-Off Treaty. Both limit the ability of states party to develop new weapons and to expand their nuclear capabilities. Third looking again at how we manage global transparency and global verification - constructing a framework that will give people the confidence to make deeper cuts in their arsenals and, one day, to give up their nuclear capability for good. I HAVE said that I want the UK to be a "disarmament laboratory." That means new thinking. So, for example, we will participate in an in-depth study by the International Institute for Strategic Studies on the requirements for the eventual elimination of all nuclear weapons. And we will back that up with practical work. We will concentrate on the complex but pivotal challenge of creating a robust, trusted and effective system of verification that does not give away national security or proliferation sensitive information. Mine is a generation that has always lived under the shadow of the bomb. But there is a danger in familiarity with something so terrible. If we allow our efforts on disarmament to slacken, if we allow ourselves to take the non-proliferation consensus for granted, the nuclear shadow that hangs over us all will lengthen and it will deepen. It may, one day, blot out the light for good. We cannot allow that to happen. The writer is British foreign secretary.