What difference could Britain make with Iran? What difference can we make in Afghanistan? What difference have we made in Iraq?

Argument about all three has flared across the past decade. Succeeding ages will be astonished at how the debates dominated our daily news. They returned again and again to Britain’s relationship with the United States. There have typically been two sides. The “ayes” have saluted US foreign policy, anxious that we should “stand alongside” America in countering what they and Washington see as threats posed by terrorist movements and other malign foreign powers. These ayes believe British interests and those of the United States are usually close.

The “noes” have argued for an independent British foreign policy that “stands up” to America and actively opposes US policies that they see as wrong-headed.

I’ve been an instinctive supporter more of the noes than the ayes. But I now want to advance an argument that will please neither. The case is, for a post-imperial nation with lingering imperial dreams, the hardest policy of all: the admission of impotence.

In Afghanistan we’re losing, however just the cause. In Iraq neither we nor even the US will in the end have made as much of a difference (for good, as the hawks would have it, or for ill, as the doves say) as both sides to the debate believe.

And in Iran I suspect the Americans are on the brink of making a huge mistake, but that we may as well sit back and let them. We have no power to stop this confrontation now. In a range of big foreign policy questions it is time we British embraced the politics of impotence. We should save our enthusiasms, our money, our international friendships and our soldiers’ lives, for what is doable.

Afghanistan is not. On Monday, November 5, Panorama on BBC One will show Taking on the Taleban: The Soldiers’ Story: not a crusade for or against Britain’s efforts, but a first-hand account of what we’re up against. Watch it and make up your own mind.

Paddy Ashdown seems to have decided already. A stalwart supporter of the British military campaign in Afghanistan, Lord Ashdown, who is by no means an instinctive defeatist about the possibilities of intervention, now believes that Afghanistan is “lost”. He contends that we could have won had we and our allies put more in, early on. Perhaps. But we didn’t. Now we are at loggerheads with the Americans about the whole philosophy of nation-building there, and hopelessly underresourced in the Helmand province, which we try to control. Counter-narcotics has been an unmitigated disaster (the opium trade has more than doubled), and though we can win set-piece battles with Taleban forces, we seem powerless to consolidate what we have won.

I loved Afghanistan when I went there for The Times some years ago. I fell under its spell. But I was conscious even then of a vast and intricate web of human groups, feuds, ties, revenges and obligations, and an incredible fierceness in the air; and of how small were Nato forces, and how limited our understanding, in the face of such vastnesses of history and geography. I was conscious too that the Taleban is a way of thought first, an army second, and infinitely renewable. I wondered if we were out of our depth.

I am sure now that we must be, without a comparable commitment from others. We should be honest about that. If the rest of Nato is unwilling to do the heavy lifting, we should give up.

I did not love Iraq when I went there for The Times, but saw that there, too, we were in too deep for our capabilities and perhaps for our understanding. Now we British have effectively abandoned Basra. The Americans say they are winning farther north and in a sense they are: US casualties are falling and so are Iraqi civilian deaths. In time they will fall to a level allowing Washington to claim some kind of a victory and go.

The truth is that the American occupation did not cause this bloodletting, though the invasion triggered it. The coalition hanging on there was always extraneous to the deeper tensions and clashes of interest and history upon which the monster Saddam Hussein kept the lid. These are resolving themselves in the way they were inevitably going to: the Shia (themselves an assortment of factions) are assuming the predominance that force of numbers always supported. The Sunni (equally riven) are beginning to worry more about the Shia than the Americans, and are doing deals and moving into the background. Next, the Shia factions will have to fight it out between themselves. Britain’s second fiddle to the American presence has made no difference at all.

Except, as in Afghanistan, to the Exchequer, to yours and my taxes, to the many families of our fallen soldiers, and to Britain’s delicate but serviceable stance as a broker among Western nations with ties of sympathy and understanding with both the nonaligned world and with the United States. This stance has been wrecked.

I don’t and didn’t advocate (as many on the anti-war Left have done) a total rupture in Britain’s relations with America. Start – as I suggest – from the premise that Britain can achieve little on the front line alongside the United States, and it may strike you that we can achieve little by inveighing against them either. The aim of British diplomacy should have been to walk the fine line between sycophancy and insubordination, as a Labour Government under Harold Wilson more or less succeeded in doing during the Vietnam War.

The next challenge will be Iran. When regional experts differ, who am I to canvass a confident opinion on whether America’s aggressive posture towards the Revolutionary Guard, leading today to sanctions, and tomorrow perhaps to a military strike, will help to entrench the power of extremists in Tehran, or help to dislodge them? My guess is that it will entrench them; the policy looks dangerous; but on the basis of such a guess, should Britain or Europe provoke an open split with Washington? To what purpose? Could we head the Americans off their chosen confrontation? Surely not. Is Britain’s trade with Iran important enough for either, to alter the argument? No.

So Britain should do here what we should have done before the attack on Iraq: give the world to understand that we are unpersuaded that the time is ripe for confrontation; but that we will not try to undermine a key ally, America, that has taken another view. We should sit this one, like that one, out. We are, anyway, impotent.

A columnist advocating that we duck an international dispute realises how unimpressive the argument sounds. It hardly stirs the blood. It lacks the ring of moral certainty. But are our soldiers’ lives worth the ring of moral certainty that comes with a bold but doomed decision to try to make a difference? I suggest a braver decision: to admit that we cannot.

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