The chances are that yesterday will prove the last Christmas Day that significant numbers of British troops celebrate the occasion together at Basra airport. Most of the present contingent will probably be gone well before this time next year, leaving behind a few specialist colleagues to assist in the training and development of the Iraqi armed forces. The festive meal enjoyed by British soldiers in the Afghan province of Helmand, by contrast, is likely to have many a successor. A substantial deployment will certainly be in that country next December and it would be no surprise if thousands were still stationed there into the next decade. Afghanistan has, therefore, surpassed Iraq as Britain’s principal overseas commitment. British foreign, defence and international development policies and budgets have to reflect explicitly this change in priorities.

The case for a British presence there is no less strong than the engagement in Iraq but should be less controversial in domestic politics. Few would deny that Afghanistan was the base from which the September 11, 2001, atrocities were masterminded, or that before that point the Taleban regime had shown itself grotesquely intolerant at home and a serious menace to international order, or that the return of the Taleban, even in limited form, to authority in that country would endanger the peace of the world. British soldiers are thus at the heart of what is a significant and direct conflict – largely fought in the open and not in the twilight through insurgent tactics – and although UK casualties have been more extensive than desired, the damage inflicted on their foes has been far higher. This is by no means an unwinnable campaign for the military.

It is one, nonetheless, that demands relentless candour from the ministers who have authorised it. Matters were not assisted at the outset when John Reid, then the Defence Secretary, raised the possibility of the mission being completed without a shot being fired. Des Browne, his successor, is asserting currently that British troop levels will remain at their current mark of a little under 8,000 men and will not be increased automatically as Basra airport is abandoned. If everything were to proceed smoothly throughout Helmand in 2008, it is possible that this prediction would be realised. It would surely be better, though, to prepare the public for the more awkward prospect that more troops will soon be required and put the Treasury on notice that although this extra demand on spending comes at an inconvenient moment, it cannot be ignored.

Along with candour comes the need for robust realism. The social and economic reconstruction of Afghanistan is a notion well beyond anything that is being undertaken in Iraq. In many instances the very word “reconstruction” is inappropriate, in that it implies that something previously existed, was demolished and can be rebuilt. Nor is Afghanistan a paradigm prospect for democracy promotion. Loyalty to the clan will always matter more than whatever political institutions are created in Kabul. The international community, assisted by Britain, can and should strive to establish a basic economic infrastructure and ensure decent primary schooling for most Afghan children. It should aim to stop the flow of illegal opium to the outside world. Anything beyond that must be deemed a bonus. It will take many a Christmas to achieve even this.