Andrew Lansley: The justification for this confrontation is built on sand

The contrast with the Gulf War in 1991 could not be plainer. The use of force then was clearly justified

As a Conservative, I believe in upholding law and order. I respect that no less in the difficult circumstances of international law than I do at home. I also understand that foreign policy must always be driven primarily by the pursuit of our vital national interests while building international institutions better able to secure peace and security. War with Iraq now could damage both.

My views on this are at odds with that of my party's leadership. We respect each other's views. Iain Duncan Smith last Sunday said that this was too important an issue for party politics. That is my authority, too, for believing that MPs were right to behave according to their own conscience and individual judgements yesterday.

While the threat of force led Iraq to allow weapons inspectors back, the use of force must be a last resort and should be given specific approval by the Security Council. The legal authority to go to war now is questionable, but, more importantly, I question the wisdom of acting when every other option has not been exhausted and international opinion is not with us.

The contrast with the Gulf War in 1991 could not be plainer. The use of force then was obviously justified. Kuwait and its allies, led by the United States and ourselves, had an absolute right of self-defence. No further authorisation by the United Nations was needed. However, the US and the UK sought and secured specific authorisation. Writing in The Search for Peace, Douglas Hurd, then Foreign Secretary, said there were hazards in this course, not least the risk of Russian or Chinese vetoes. But diplomacy won and, as Hurd said, "The specific approval of the Security Council was a necessary condition of Allied success." In 1991, we had a clear UN mandate, equally clear aims, and a broad international coalition. This included support from Arab states, extending to Saudi financial backing.

The British Government's proposal to use force now is a response to a failure of diplomacy. Far from strengthening the authority of the United Nations, as the Government claims, the unwillingness even to seek a further specific authorisation has damaged UN authority. In the process, great damage has been done to relations within the European Union and beyond.

I supported the Government in previous Commons votes on Iraq; I always did so on the basis that having chosen the UN route last autumn, we would persist in that. Indeed, the British Government, by tabling draft resolutions over the last fortnight, explicitly accepted that there was scope for Iraq to be given one further, short period in which to demonstrate the active unconditional co-operation necessary for the weapons inspectors to complete their disarmament tasks.

Of course, inspection without Iraqi co-operation would never produce the full disarmament required. But there is a perversity in the approach taken by Britain and the US, which has failed to recognise that the enhanced weapons inspection since last November has given substantial evidence of the extent of Iraqi non-compliance, gone a considerable way to destroying equipment, especially missile technology, and defined the disarmament tasks which remain.

The logical, and wise, next step, would have been to require Iraqi co-operation in those defined tasks, recognising that it takes only days for the Iraqi regime to demonstrate active co-operation, even if it would take months thereafter to complete the disarmament process itself.

There may be those who would never countenance the use of force to compel Iraq to disarm. I am not one of those. But we must live within a framework of international law. If we do not, we will make the risks of unilateral military action greater. As John Major said of the decision not to go on to Baghdad in 1991: "If the nations who had gone to war on the basis of international law were themselves to break that law, what chance would there have been in the future of order rather than chaos?"

The justification for this war is built on sand. Iraqi links to international terrorism are asserted but not sufficiently substantiated. Regime change is not the ostensible purpose but the ultimatum to Saddam Hussein suggests that it is. And President Bush's address to the US public suggests the exercise of a pre-emptive right of self-defence, but that is not authorised by the UN.

One thing will be constant: the courage and professionalism of our armed services. They do the job asked of them, and have our support and appreciation for the way they do so. They know that the debate over policy is no reflection on their position; they will be acting against an evil regime and the Iraqi people may well be the long-term beneficiaries of their action. I hope that they, and international peace and security, do not suffer the harm that I fear.

The writer is the Conservative MP for South Cambridgeshire