At last, amid all the bleak news that comes from Afghanistan, there’s a success story to justify the British and American presence there.

Because one of the main aims of Western intervention in foreign affairs is to establish the sort of small-business, entrepreneurial spirit that can rescue a struggling economy. And according to the United Nations, there’s been another 18 per cent growth in the heroin trade, in just the past year.

It goes to show that, even in the most difficult circumstances, with a popular product and thoughtful marketing, there are always business opportunities for those with a flair for entrepreneurial vision. At the time of the initial invasion in 2001, Tony Blair insisted that one of the reasons for occupying Afghanistan was because “the Taliban are causing the deaths of young British people who buy their drugs on the streets”. But clearly some people misunderstood what Blair meant. They were saying that the Afghan heroin trade wasn’t fulfilling its potential, and with the right management they could treble it.

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It will probably turn out Blair is getting £4m a year to sit on an advisory board to help them maximise growth. Spokesmen from companies with names like Kwik-Fix Global will appear on the business section of Sky News, explaining how their quarterly report reveals a 35 per cent rise in dividends, boasting about surveys that show that the Afghan brand earns positive feedback with 95 per cent of junkies, and hinting at diversification into other markets such as its own brand of needles so customers can enjoy the full Afghan warlord poppy experience.

Maybe the plan is that, by the time British troops leave, every district of Afghanistan has a thriving garden centre, where couples from Helmand province can potter around on a Sunday, arguing about which seeds will produce the most effective skag and enquiring about how to set up a poppy rockery.

Then there’ll be an Afghan Gardeners’ Question Time, with the audience asking: “This year, my poppy window-box became susceptible to mildew around springtime, so the opium was disappointingly soggy and hard to burn in the spoon. Has the panel any suggestions for how to prevent a recurrence?”

It could be claimed that the growth in heroin production would be even greater if the occupying forces hadn’t been in the country. But this would be to deny them the credit they’re due. Because it was also revealed this week that the office of Afghan leader Harmid Karzai has been regularly receiving envelopes stuffed with cash from the CIA, for the past 11 years. The New York Times reported that the money has come in “backpacks, suitcases and plastic bags”.

The allegations are denied by a Foreign Ministry spokesman, but Karzai explained the purpose of these payments was to “secure the support of those leaders who have been loyal”. One of the other reasons for the invasion, you may recall, was to stamp out corruption. That makes sense, because you can’t stamp out corruption without the support of honest, reliable officials, and you can’t expect them to stay honest and reliable for nothing so it makes sense to hand them envelopes stuffed with cash every couple of weeks.

The people the money has been handed to are local warlords, who won’t stay loyal unless they’re also allowed to carry on their legitimate business of growing poppies, so it all completes a neat business circle. To make it seem even more like a typical business arrangement, some of them have complained that the amount that the local farmers receive for their poppies is only 1 per cent of the eventual market value. You’d think that at least our Government would insist on an ethical poppy policy, encouraging dealers to pay a decent price so they could stand behind the bins on a council estate wearing a sticker saying “All our smack is Fairtrade”, next to a picture of a smiling warlord.

Once you add in the other reasons for occupying the place, the scale of the occupation’s success becomes even clearer. There was the Taliban’s “appalling record on human rights”, whereas Saudi Arabia, with which we’ve just concluded a £15bn arms deal, is just a constant hubbub of feminist this and lesbian that.

It is so liberal that it’s the only country where women get no extra penalty if they’re caught drinking and driving, as they get put in jail for either so they might as well do both at the same time. And the invasion was supposed to stop Afghanistan being a centre for al-Qa’ida, which has gone exceedingly well. Because now Afghanistan is only one place for the militant Islamist organisation, as they’ve grown in Iraq, Iran, Syria, Mali, and a variety of places where they didn’t exist before. Once they’ve taken control of Dorset County Council, I suppose the job will be complete.

When British and US forces first occupied Kabul in 2001, there was jubilation from those who’d supported the invasion, especially those who saw it as a humanitarian policy. Some day soon, I suppose they’ll accept it hasn’t all gone to plan as much as they thought. Or they might stick it out, following the Government’s line that we’re leaving because we’ve done an excellent job, and now the Afghans we’ve been giving stuffed envelopes to have learned enough from us that they can carry on from here.

If only Napoleon had thought of this tactic. He could have said: “Right, it’s all gone very well, but, if you Russians don’t mind, we’ve got other stuff to get on with, so you’re jolly well going to have to get on without us. Bye then, thanks for having us.”

Twitter: @mrmarksteel