Dictators who gas their people must feel the consequences: that is the basis of our security

We were warned. Earlier this year, the Security Services told Parliament’s Intelligence & Security Committee that “the most worrying point about our intelligence on Syria’s attitude to chemical weapons is how low a threshold they have for its use.”

But the Committee’s report came in July. The sun was shining; no-one wanted to talk about a problem with unpalatable solutions. This was just a civil war, they said, the latest instalment of a sectarian dispute. The ongoing humanitarian crisis failed to trouble our consciences. In the silliest of seasons, there was more interest in the salaries of charity chief executives than in the lives the aid organisations were trying to save.

Now we have no choice but to face up to what is happening. We managed to ignore nearly two million refugees and 100,000 deaths. But there is an inescapable logic for drawing a red line on the use of chemical weapons whose deployment represents a threat of a different order.

The Intelligence & Security Committee also said that the security of Syria’s chemical weapons stocks was a “serious concern”: if these fell into the hands of terrorists, the consequences could be “catastrophic”. Perhaps, having ignored the first of the Committee’s warnings, we might now pay attention to the second.

The justification for action now is not outrage at the suffering in Damascus, terrible though the scenes are. It should turn, first, on the need to deter the use of chemical weapons in future and, second, to ensure that such weapons are not obtained by extremists who will never be deterred.

The West’s security relies on credible positions that egregious international actions will have certain consequences. Iran will test our stance over its development of nuclear weapons, and that regime is deeply insinuated in this crisis. Red lines cannot casually be crossed. If Israel took the same attitude to its red lines as our more hesitant politicians, the country would no longer exist.

The House of Commons may be persuaded that the use of chemical weapons requires a response, but only because the Government has carefully not broadened the argument into one for wider intervention. MPs quickly balked at the first suggestion, made earlier this year, of arming Syrian rebels.

Critics of military intervention complain that the West has no strategic objective. But we do. We’ve already declared that Assad should go through a negotiated settlement; we want moderates to assume power, and we don’t want jihadist insurgents to win out. It’s not an objective we lack: it’s the will to achieve it. For two years the West has been speaking loudly and carrying a small stick.

The argument that this conflict has nothing to do with us is extraordinarily short-sighted. We have every concern in the stability of the region, as the critics of military action quickly note, and in ensuring that extremists do not take hold in Syria or acquire weapons of mass destruction. Questioning whether military action will improve the situation is one thing, but to deny any British interest would be an abrogation of responsibility.

The problems of intervention are real enough, beginning with Russia’s opposition, which is founded on their fear that overthrowing Assad will merely hand rule to extremists. Our job should be to prevent that happening, not sit back and hope it doesn’t. Russia may choose the rule of despots in the Middle East to ensure that jihadis do not surface, but the West should not be so sanguine that the Arab Spring is giving way to democracy’s fall.

Of course it would be better to act with full UN approval, but Russia is hardly neutral in this conflict: it is arming Assad. NATO’s action in Kosovo was taken without UN approval, yet it saved thousands of lives. The UN failed to prevent genocide in Rwanda where earlier US action might have succeeded.

In the end, none of the claimed obstacles have been the real brake to action in Syria. It is the military interventions in Iraq and Afghanistan that have made the public and politicians queasy about new action. And so, twelve years on, the shadow cast by 9/11 lengthens.

But we do not need to be paralysed by the legacy of Iraq. Unlike Saddam, Assad actually has chemical weapons. The public backed military action in Libya which was targeted, taken with Arab League support, and with the immediate objective of preventing a massacre in Benghazi. No-one is proposing a ground invasion of Syria.

It certainly isn’t enough to assert that ‘something must be done’ without thinking through the aims and consequences of action. But saying that nothing should be done in the face of a national security threat and a humanitarian disaster is the worst of all stances.

The minimum requirement now is for a swift and carefully targeted missile strike against Assad to underline the West’s stance against chemical weapons. Britain must stand with the US and France on this at least.

We cannot keep ruling out any kind of military intervention while watching Assad’s grip tighten and the jihadis gain strength. How else will he brought back to the negotiating table? Assad needs to be given an exit route, but at present he has little incentive to take one. We will not even arm the moderate rebels, despite their pleas. The danger of weapons falling into extremists’ hands has only increased with each month of Western indecision.

The House of Commons has awoken and been recalled from the summer recess not to demand action in the face of atrocity, but to assert its right to authorise military intervention. Now we have to decide what to do. If we decide merely to be good men determined to do nothing, we should have stayed at home.