Five years on, let us take the high road. When the invasion of Iraq was conceived, it was as an experiment in the transforming force of a confident superpower; an evangelistic Tony Blair trotted on behind. Removing a dictator was only to be the start; the objective was a benign and democratic Middle East – an environment in which Israel and the Palestinians could make peace, and energy exports were plentiful and secure.

Even now, the removal of that dictator remains the single attainment of an enterprise that was always as flawed in its genesis as in execution. Iraq is a war-torn and wasted land. Estimates of its civilian dead range from almost 100,000 to more than 10 times as many. More than two million of its people have fled. The indiscriminate killings may have slowed, but ethnic cleansing continues apace.

Any semblance of democracy is confined to the Kurdish region – as it was before the war. The government and parliament are corralled in the Green Zone, walled off from the citizens they are supposed to serve. Neither the central government, nor the 150,000 US troops, have been able to match even the inadequate supplies of power and clean water that Saddam Hussein made flow in his day. Iraqi police and armed forces are still nowhere near up to standard or strength.

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Over five years, the US has lost almost 4,000 troops, with 30,000 wounded – a toll of grief and suffering that is already influencing the course of US politics. At 175, the number of British dead might seem modest; as the price of involvement in a war that was unjustified and unnecessary, any figure would be too high.

Nor is the south that we British have handed back to the Iraqis the model of peace and tolerance that we had hoped to bequeath. Plagued by warlordism and riven by sectarianism, it is now left pretty much to its own devices. Yet they are still seen as holding a necessary line, now that the rest of the foreign coalition, such as it was, has departed. The Poles and Australians were the last to leave – both essentially voted back by disgruntled domestic electorates.

A RESURGENT IRAN

The US, for its part, is trapped. The controversial troop surge briefly subdued the violence – but at tremendous cost in men and material. With the effect wearing off, however, Washington can ill-afford to reduce their numbers, lest the violence return to previous levels. And their necessary visibility places them at greater risk. On the plus side, then, the demise of Saddam Hussein. On the minus side: thousands of deaths, the proliferation of suicide bombings, no great groundswell of democracy, still less energy security, and a resurgent Iran – youthful and militant – sweeping into the power vacuum left by Saddam. On the world stage, both the US and Britain are smaller countries.

Five years on, the totality of our failure is clear. But worse even than that failure, perhaps, is the obstinate refusal of our political leaders to learn the obvious lessons. Of course, any lingering shreds of idealism are long gone. On becoming Prime Minister, Gordon Brown changed the Government's tone to one of sombre realism, rather than messianism. And for a brief spell, he drew a distinction between the operations in Afghanistan and Iraq, rather than dishonestly conflating the two. That did not last. And the promise of a parliamentary vote on any future war, while good for a headline, is of limited value. There was a parliamentary vote on Iraq: the problem was not the lack of a vote, but the lack of an opposition.

On both sides of the Atlantic, however, political leaders still insist that the war was the right thing to do. If there were errors – and they admit there were – they were all in the implementation, not the enterprise itself. Nor, in official parlance at least, does the appetite for using armed force seem diminished. Mr Bush persists in threatening Iran with armed force, despite overwhelming evidence that his military is overstretched, while the British foreign secretary gives gung-ho speeches on the misunderstood merits of armed intervention.

In his Budget, Alistair Darling announced the higher military budget as though he was talking about new social spending, rather than the – very high – price of Mr Blair's Mesopotamian adventure. In terms of manpower and money, we have acquired a long-term obligation in Iraq. The true cost has still not been honestly acknowledged.

INQUIRY NEEDED

Meanwhile we await the comprehensive inquiry into how we got into Iraq – into the decision-making involved, the intelligence debacle, and the rest. Mr Brown's recent promise of an inquiry when the troops are home is a small step in the right direction – at least he recognises that such an investigation is desirable – but it disgracefully, and perhaps indefinitely, postpones the day of reckoning.

There are those, of course – an increasing number of self-justifying memoir-writers among them – who maintain that five years is but the blink of an eye in the greater perspective of history. The worst, they suggest, is over, and a new, modern Iraq will then arise from the blood and ashes. We hope against hope that it will.

The evolution of a new Iraq, however, will be proof not that might was right but of the indomitability of the human spirit. We would also remind those tempted to regard these five years of suffering as somehow vindicated that the timescale Mr Bush envisaged for operations was rather closer to five months.