By the time this article is published Iran will either have issued a belated response to the package of incentives put forward by the five permanent members of the Security Council and Germany in June, or be on the point of doing so. These proposals were intended to persuade Iran to freeze its nuclear enrichment activities and return to the negotiations it abandoned in 2005. Iran has said it will not suspend its enrichment programme. It has suggested that it will not give a simple "yes" or "no" to the package: instead the reply will be "multi-faceted".
In the meantime, the Security Council has passed a resolution warning that no further delay will be tolerated and that Iran must suspend its enrichment programme by 31 August or face the prospect of sanctions. Iran's behaviour so far suggests it will neither accept the incentives package nor yield to the Security Council. Last month it cancelled a key meeting with the EU foreign policy chief, Javier Solana. When the meeting was rescheduled, the Iranian representative reportedly merely repeated formulaic statements of the Iranian position.
Throughout its dealings with the international community over its nuclear programme Iran has relied on a selective reading of the Non-Proliferation Treaty, emphasising its rights but glossing over its duties. It has sought to pit itself as a champion of the developing world against a new form of western colonialism, and to cultivate ambiguity about the progress of its programme. It has denied that entirely proper decisions of the Security Council are legitimate. This will, the Iranian government judges, make it much harder for the world to agree on a response. In the meanwhile it has rushed ahead with its enrichment programme in an attempt to create nuclear "facts on the ground" and in the hope of presenting the world with a fait accompli.
Iran persists in its belief that it also has the power to undermine legitimacy in Iraq, Afghanistan, and Lebanon; fostering division in the international community and buying time for its efforts to cross the nuclear threshold - the mastery of the technology of enriching uranium which can, and in Iran's case will, lead to a weapons capacity.
The 31st of August will therefore mark a critical moment for the international community's resolve. In the past the Security Council members have failed to overcome their differences over enforcement action. However renewed tension in the Middle East following the conflict between Israel and Hizbollah, and the undeniable involvement of Iran in arming and supporting Hizbollah, makes it more urgent than ever that the Security Council Members show strength and unity of purpose. In this contest of wills it must be Iran that is made to back down, not the Security Council. Pressure has to be put on Iran now. In order to do so, the choice facing Iran must be made real and painful, not theoretical and distant.
It is time the British Government, in conjunction with the United States, supported specific measures against Iran if it fails to comply with the Security Council resolution. These should include banning nuclear co-operation with Iran, halting the sale of dual-use nuclear technology and military technology to it, and prohibiting new international investment in oil and gas projects in the country.
There is not much chance of applying serious pressure on Iran while some permanent members of the Security Council, for example, continue to sell large quantities of military technology to the Iranian government. Russia alone will provide $1bn in defence technology to Iran, including TOR-M1 surface-to-air missile systems, in an agreement sealed last year. Russia is also by far the largest contributor of nuclear technology to Iran, which will be looking for continued Russian support if it is to acquire the nuclear technology and expertise it needs. Britain, France and the US have worked hard to create a united front with Russia and China. Now it will be put to the test.
As the Iranian regime feels a net closing it is likely to seek to lash out where it can. We may have to face disruption to the oil market and further subversive activities. The Security Council should make it clear to Iran that while it will hold open a return to negotiations at any point, it will not be deterred.
The stakes could not be higher. The viability of the Non-Proliferation Treaty is in jeopardy if Iran succeeds in cheating it and acquiring nuclear weapons. If a regime which has declared its wish to see Israel wiped off the face of the map obtains those weapons, so too is the peace and stability of the Middle East and the world.
The writer is shadow Foreign Secretary