On Wednesday Gordon Brown outlined his latest strategy for Afghanistan, by announcing a temporary increase in troops, additional funding to tackle poverty and promote education, and an increased emphasis on training the Afghan army and police force. The greatest weakness in this new approach is that it does not plausibly answer the first question that enters the mind of any Afghan when he sees foreigners in uniform.
That question is "When are you leaving?"
This should not be a surprise in a country that has received and expelled so many invaders in its long history. It is a question that arises partly from pride, but also from self preservation. The fate of any Afghan that miscalculates who will be around in ten years time is impoverishment, oppression, and possibly death, for himself, but also for his family.
Which leads to the second question, which is "What will you leave behind? Who will be in charge? Will he last? Will his writ run beyond the suburbs of Kabul?"
In other words, how are you going to guarantee the effective survival of the central state in a country where it more often than not fails, and where few people are really aware of its existence.
The answer given by the Prime Minister was, in truth, spectacularly inadequate. The single most important issue is the security of the state. The guarantor of that security cannot be foreign, it must in the long run be Afghan. It must also be powerful.
Now compare the reality of today's Iraq with the proposed future for Afghanistan. Iraq is smaller, less complex, richer, and better educated than Afghanistan. It has a stronger history as a stable state. Today it requires 600,000 security forces to maintain its fragile integrity. Yet Gordon Brown seems to believe that Afghanistan, with its history of lawlessness, its civil wars, its drugs trade, and its meddlesome neighbours, can prosper on a total security force of some 200,000 men
What is more, about a third of those security forces are expected to be policemen. The Afghan National Police are not just a poor instrument of law and order; they are an active agent of criminality.
Two thirds of them are drug addicts, and the majority are deliberate criminal oppressors of the ordinary Afghan. Systematic extortion, kidnap, theft, and rape are their stock in trade. So they do not add to security, they subtract from it. At least three quarters of the force is beyond recovery, and the best option is likely to be to start again, with a completely new force. That is not to say the task is impossible.
The Afghan National Army is different again. A conventional soldier might be horrified to watch their casual behaviour. They have faults – occasional cruelty, tribalism, variable leadership, but they are manageable. To have a chance, however, there will need to be at least four times as many as is being proposed. Without that sort of number, Afghanistan will revert to a lawless, drug-ridden bolt-hole for terrorists and insurgents. The Taliban will win, and al-Qa'ida will be the beneficiary.
We must persuade the Afghan people that we are creating a viable, long-term Afghan security solution. We must answer the question "what comes next" in a way that stops the current slow but inexorable drift back to the Taliban.
A proper Afghan security force will be expensive. The annual subsidy would need to be about $3 billion, and that is after the upfront training costs. However, it will be cheaper, in blood and treasure, than the alternative ineffective endgame, and it will offer an exit that is better than the humiliation that is currently on the cards.
Furthermore, it is not essential that Britain and America shoulder the entire burden. So far ISAF, the International Security Assistance Force, has been pathetically incompetent. One American journalist in Kabul described it to me as a "combination of nations, some of whom can't fight, and some who won't fight."
While this is unfair to some nations, it is broadly right. We would do better to persuade its allies to help with the financing of the Afghan security force, and give up on (most countries') expansion of military support. That may make the long term costs more bearable, and also reflect the importance to the whole world of bringing both drugs and terrorism under control.
We stand at an historic crossroads on this. If we are (a lot) tougher on the corruption of the Karzai regime; ensure delivery of justice on the ground, even if it is tribal justice; and create a security force that underpins a viable government, we stand a chance of delivering what no foreigner has ever done before, namely a successful Afghan state. If not, we will be allowing the waste of countless lives to achieve little more than Vietnam.
David Davis was shadow Home Secretary, 2003-2008