The importance attached by Nato to success in the battle for Musa Qala is justified. The assault, which started on Friday, matters for its strategic value, but even more because the town has become a symbol of the Taleban’s ability to resist Nato and Afghan forces.

Musa Qala is the only town in Afghanistan undeniably under the control of Islamists. It is also a crossroads for the opium trade, which Western forces fear is paying for the insurgency. It took on those twin roles when Britain handed over its control to local Afghan leaders, who failed to keep out the Taleban as they had promised.

The Taleban have extracted huge propaganda value from the failure by Nato and Afghan forces since then to chase them out. Britain has also suffered a blow to the central plank of its strategy: to hand over control of towns and provinces to Afghan forces. It needs to show that the strategy can hold good if it is to make almost any kind of progress across the country.

Britain, with the largest contingent of forces in the south, and with prime responsibility for tackling the drugs trade (after the Afghans themselves, British ministers are always careful to add), has had some local successes in Helmand province. Its strategy – after six years of many false starts – is also becoming more coherent, with the military drive to secure towns working more closely with the development projects aimed, in a phrase particularly overused in Afghanistan, at winning hearts and minds.

But while British ministers have described the political and social development of Afghanistan as a 20 or 30 year endeavour, military commanders – notably Lieutenant-General David Richards – have said that the Afghans’ patience for any foreign presence will run out in a few years if there are not more tangible signs of progress.

Several factors have come together to make it imperative for Nato to reclaim Musa Qala now. The blooming health of the opium trade, more exuberant year after year, is more than an embarrassment; it is a measure of the failure of parts of the strategy, as well as a threat to it all. The weakness of the Government of President Hamid Karzai is a second; his imperfect support of Nato efforts, his faltering grip on parts of the country, and his desire to talk to those close to the Taleban to try to shore up that support has imparted even more urgency into Western efforts. Iran, while broadly helpful in tackling the drugs trade, is in no mood to help the West to win in Afghanistan, and accusations that it is actively helping the Taleban, even though they were its former enemies, flicker through British-Iranian relations.

Above it all hangs the uncertainty of Pakistan’s Government. Without the support of Pakistan, the Nato battle in Afghanistan becomes near unwinnable, many think. If there is a grievance that unites Pakistani politicians and generals, it is their belief that Pakistan has been given too little credit by the West for its struggles to defeat the Taleban on its side of the border.

President Musharraf and Benazir Bhutto, the former Prime Minister, both of a secular and liberal persuasion, maintain that such efforts will continue even without Western plaudits, because of Pakistan’s own need to defeat its internal militants. But the same cannot be assumed of Nawaz Sharif, another former Prime Minister, who took the country in an Islamist direction in his time and freely did deals with the religious parties to strengthen his power base.

It would help Nato’s campaign – and the wider Western efforts to foster government in Afghanistan – if the battle for Musa Qala were decisively won before these new threats became real.

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