Leading article: Without the numbers, we must lower our sights

We must hope the Ministry of Defence is right to assert a technical fault brought down the RAF Nimrod in southern Afghanistan on Saturday, rather than a surface-to-air missile fired by the Taliban. However, we must also admit that whatever the truth concerning this tragedy, the Taliban will use it to advertise their claim that the British are now on the run.

The operation in Afghanistan always depended on a degree of bluff, on what the old Empire-builders called "showing the flag", which meant convincing the mass of uncommitted waverers in the population that they represented might as well as right. Now, those waverers are in greater danger than before of tactically switching their allegiance back to the Taliban as the most likely winners of the struggle to control the country.

This depressing turn of events, from a British military point of view, comes as a UN report reveals disturbing evidence of a vast upsurge in opium production in Afghanistan, precisely in those southern provinces where British troops are under most acute pressure. The report says production has jumped by about 60 per cent since last year and is now responsible for more than one-third of the country's economic activity.

This poses yet another unwanted challenge to British troops. Not only are they struggling with the military task of subduing, or at least holding back, the increasingly organised Taliban in the villages. At the same time, they are expected to police the region as well, and to destroy the poppy fields on which it is clear a growing number of Afghans depend for their livelihood.

This is a deadly matrix, and the deaths on board the Nimrod, following the bloodiest month for the British in Afghanistan since the invasion began, suggest it is only a matter of time before what has been described as a "forgotten war" is forgotten no longer.

It is now clear is that two insufficiently thought-out foreign policy initiatives, Iraq and Afghanistan, are in danger of converging as an arc of failure, a development that threatens to leave the five-year American and British-led "war on terror" in terrible disarray.

In Afghanistan, government officials in London have waged a conflict with deep delusions in mind. One was that the mere presence of a handful of British troops in the turbulent south would be enough to scatter the Taliban. Another was that opium production could be depressed without massive foreign investment in Afghanistan on such a scale as to provide rural farmers with tempting economic alternatives. Overall, the strategic error was to go into Iraq in 2003 without having followed up the previous invasion of Afghanistan and established the authority of the new pro-western government in Kabul.

Too late now to rewind that particular tape, of course. We are where we are, embedded miserably in both and with diminishing hopes of an orderly exit from either.

What then to do? The first sign that realism may be dawning would be an end to implausible slogans about victory "around the corner". The second, deeply distasteful as this may be, would be to redefine what we can practically expect to achieve in this country.

Without a massive insertion of fresh troops, which Iraq and defence cuts rule out, we may have to accept we cannot control the southern provinces and tactically retreat. Some strategists will shiver at that, raising parallels with Vietnam, where withdrawal to Saigon and other cities merely whetted the Vietcong's appetite.

But if British losses mount, calls will inevitably grow for us to abandon a struggle that seems merely to expose our troops to the danger of needless loss of life, without actually altering the eventual outcome.