IN 1842, Britain's retreating forces in Afghanistan were all but wiped out when the Kabul cantonment seemed impossible to defend.

In 1879, the second of the Afghan wars kicked off when the British representative was murdered by native troops. In the third mad conflict, commencing in 1919, the locals had to be bombed into submission before victory could be declared.

Where Afghanistan is concerned, history is as unambiguous as it gets. Each of those imperial wars saw any number of "decisive" British victories, but the upshot was always the same. Peace was imposed through slaughter and maintained, for a while, by big subsidies to whichever corrupt local had clawed his way to power. Then everything went to hell. It is a story that has been told over and over. It was rammed home, for those paying attention, by the aftermath of the Soviet occupation in the 1980s. Invading Afghanistan is the easy part; holding what you acquire is next to impossible. Which part of this bloody tale still needs to be explained?

The Soviets were unwelcome visitors to the country for the best part of a decade. It cost them more than 14,000 killed and at least 53,000 wounded. A fortnight from Sunday will mark 11 years of effort by Britain, the US and their allies to subdue the place. In that time, 430 Britons have lost their lives amid a total allied loss exceeding 3000. The Americans have meanwhile spent more than $500 billion. Our expenditure, if you trust the official calculations, is heading towards £20 billion.

All this, yet we can no longer safely mount patrols with the soldiers of the government we are supposed to be aiding. All this, yet our troops cannot trust local police not to stage assassination attempts against their "friends". All this, for the sake of a corrupt government given to rigging elections whose motives and reliability are worse than suspect. My dictionary defines "wilful", in part, as "obstinate, headstrong... intentional". "Stupidity" requires no definition.

Yesterday, Labour's Paul Flynn was suspended from the Commons for using the only appropriate word in the circumstances. The House has its rules, but it is hard to imagine what else the MP for Newport West could have said to Philip Hammond, the Defence Secretary, about Afghanistan, Britain and Nato. We have been fed lies. The results have been lethal, for Britons and Afghans alike. The entire campaign has been as dishonest as it is futile.

The lies, for all that, are perplexing. The original American attempt to smash al Qaeda and hunt down Osama bin Laden was justifiable, if it even required justification, in the aftermath of 9/11. Since then, nonsense has been piled upon nonsense. But why, exactly?

Denying bases to terrorists when the Taliban have no extra-territorial ambitions and the real problem is in Pakistan? Building democracy under the questionable – to say the least – leadership of Hamid Karzai? An attempt by the unlikely feminists of Whitehall to secure the rights of Afghan women? An effort to eradicate the drugs trade despite unquenched western appetites? A strategy founded on the faith that Afghan forces can be trained as proxy warriors, despite America's bitter experiences with "Vietnamisation"?

It's hard to say which is more disturbing: the possibility that elected leaders have spent more than a decade believing any of this, or the probability that they have believed not a word. George Bush gave the order and Britain followed. Barack Obama decided he needed his "war of choice" and Britain followed. One incidental result, as SNP loyalists should note, is that Nato's charter and aims became collateral damage.

The various proclaimed aims were not, in isolation, necessarily malign if you believe that sometimes there is a duty to intervene. A democratic Afghanistan would undoubtedly be preferable to a medievalist Afghanistan. But the list of states in need of aid, protection and improvement is a long one. Many could have been transformed for a fraction of America's $500 billion or our £20 billion. Yet the only thing we know for sure after 11 years in Afghanistan is that a lot of locals – and not just the so-called Taliban – want us gone.

So the retreat begins. America's unilateral decision – the esteemed British allies were not warned – to suspend most joint operations with Afghan government forces is an outright confession of failure. After 51 Nato deaths in "green-on-blue" incidents, the pretence of trust is extinguished. The fiction of co-operation will end shortly. The myth that the allies will remain "until the job is done" has meanwhile only a few months left to run. It will be gone and forgotten the instant Mr Obama wins re-election.

We are supposed to believe that the new restrictions on co-operation are limited and temporary. We were also supposed to believe that Camp Bastion, the new home-from-home for Prince Harry, was the most highly-defended place in the country. That was before two US Marines and six fighter jets were lost to guerrilla action. If Nato cannot defend its chief cantonment, what can it defend?

A few conclusions need to be drawn. One is obvious: Britain would have been £20 billion better off without this adventure and Afghanistan, on the evidence, would not have been worse off. Yet we went in, as armchair generals like to say, because our politicians received their instructions from the White House. We have persisted with the folly, and suffered the losses and the lies, so that those same politicians could save face.

The rational course, adopted even now, would involve a confession. First, that hundreds of British lives – no-one counts the Afghans we are "aiding" – have been expended on a stupid and unwinnable war, one in which al Qaeda long ago ceased to feature. The politicians have known as much for years.

The second truth, still unconfessed, is more serious. It is that Britain is not, as far as America is concerned, a sovereign country. Our politicians take their instructions from a foreign power. A neat, nasty irony thus becomes evident. Professing to fight for democracy in a distant land, we have surrendered it at home.