Justice, as the cliche has it, must not only be done, but be seen to be done. By the same token, policy decisions must not just be taken - they must be declared. Otherwise their benefit is reduced or lost. As Gordon Brown visited Iraq yesterday to prepare for Monday's formal announcement to parliament on Britain's troop presence, he should ponder these truths. Some 42% of the public want Britain's involvement in Iraq to end as soon as possible, and another 22% by the end of next year, according to a BBC poll last month. The prime minister talked yesterday of a reduction of a thousand troops by Christmas, but if he says nothing specific about a full withdrawal, he will be disappointing millions of people, as well as the troops themselves.
There is an overwhelming desire among the country's military commanders for an end to the British adventure in Iraq. However professionally they acted, they were given a mission that was unnecessary and wrongly conceived. Along with the much more decisive role of the United States, this mission has helped to plunge Iraq into political turmoil and the largest human emergency in today's world.
At last week's Labour conference, neither the prime minister nor the foreign secretary were ready to concede this. Brown talked of "doing our duty and discharging our obligations", a phrase he has spelt out elsewhere by referring to UN resolution 1770, adopted by the security council in August. But the resolution makes no call on UN member states to keep troops in Iraq. It mainly asks them to provide logistical, financial or security support for the small UN staff. There is no special "duty" or "obligation" for Britain.
In his speech Miliband was full of non sequiturs. "We need to continue to support the development of an effective Iraqi security force," he said. Sure, Iraq requires such a force, but in what sense does Britain "need" to support it any more than other countries? Nor does it have to be done by maintaining UK troops in Iraq. It can be done by paying for Iraqi training, or taking officers to courses in Jordan or elsewhere. "We need to keep our promise to all Iraqis that they will have an economic stake in the future of the country," Miliband went on. Parse that piece of gobbledygook, if you will. If the foreign secretary means we have offered money for reconstruction and must deliver, fair enough, but why does economic aid require British forces at Basra air station?
It would be nice to think that Brown told the Iraqi prime minister yesterday that Britain was about to leave his country. But if there is going to be a clean break from Blair's disastrous war, it needs to be announced. A tactical case can certainly be made for withdrawing some forces by stealth. It is unwise to telegraph to militias that a unit is on its way out or will leave by a particular date. British commanders will want to keep a low profile in extracting the heavy equipment and armoured vehicles that have to go by land. Organised retreat often involves deception. Units that leave Basra air station on what looks like a routine ground patrol can end up in Kuwait, rather than returning to base. But the bulk of the troops and their kit can safely fly out. There can, and should be, a pre-announced and dignified handover of the air station, as was done when the remaining contingents left Basra city last month.
Some senior American commanders are trying to delay a British departure by hinting that Britain plays a vital role in south-eastern Iraq in safeguarding Route Tampa, the supply link between Baghdad and Kuwait. But even they concede that US troops will not be used to plug the alleged gap. They will mount more air patrols. British experts like Michael Clarke, the director of the Royal United Services Institute, question the US case. "The US operation in Iraq is self-sufficient. The US would never let themselves become dependent on the UK," he says. Nor does he believe that a British retreat would require US cover - another argument used to deter the British from going. "The mechanics of withdrawal are not as dramatic as the Americans are implying. The idea that the US would have to deploy two brigades to protect a British withdrawal is overwritten," he says.
So if Brown decides to keep British troops in Basra indefinitely, the reason will be political, not military. Either he does not accept the pointlessness of Britain's staying in Iraq, or he is unwilling to upset Bush. It is hard to know which is worse. Other Nato member states that had troops in Iraq - Spain, Italy and the Netherlands - have pulled out after realising that western outsiders can play no relevant military role in Iraq. As Britain's senior soldier Sir Richard Dannatt put it, they exacerbate the security problem.
Britain, it is true, played a key role in the invasion and has allocated more troops than other European Nato members to the occupation. Leaving Iraq now would send a more significant message. Britain was perceived as participating in what most Arabs and Iraqis saw as the latest in a long line of imperial western interventions in their region. That is why withdrawal should not be done by stealth. For Downing Street to declare that Britain's part in the occupation of Iraq is over would be the single best way of improving Britain's standing throughout the Middle East and the Muslim world.
Brown and Miliband may continue to refuse to admit that the invasion was wrong. "We will not resile from that decision," they like to say. The important thing is to recognise that Britain can make no further impact in Iraq. Basra has been under the control of Shia parties with armed militias for three years with the consent of the British military. Pragmatically, British officers saw where the local power lay and decided not to confront it. Whether these Shia militias fight or make deals among themselves is not an issue that 4,000 or 2,000 British soldiers at Basra air station can influence.
Similarly, whatever the US decides to do with its own doomed mission in Iraq is beyond London's control. There is no basis to imagine that by remaining in Iraq, Britain has some say over how long or short a time the US stays there. British politicians should take the advice of the British military. They should withdraw UK forces from Iraq completely, and do it now.