REALPOLITIK: Trevor Royle

When a military commander reports from the battlefield that victory is by no means certain, it's time to sit up and pay attention. Soldiers don't normally go all limp-wristed when the going gets tough; it's not part of their mental landscape. So, ahead of today's renewal of Nato's mandate in Afghanistan, a few eyebrows were raised when Brigadier Mark Carleton-Smith, who commands 16 Air Assault Brigade, claimed that the war was unwinnable. Coming on top of a similar admission from Britain's ambassador to Kabul and followed by a later comment by US defence secretary Robert Gates that Nato will never get the upper hand against Taliban insurgents, it makes one wonder if the alliance's strategy is finally unravelling in that troubled country.

Of course, it is doing no such thing. Carleton-Smith was simply stating the obvious: that no war of this kind can ever be won by military tactics alone. As has become blindingly clear over the past couple of years, Nato ground forces will always get the better of the Taliban in a square-go - well, at least they will if they are American, British, Canadian or Dutch, who provide the bulk of the frontline troops.

For all that Taliban fighters display fortitude, endurance and undoubted personal courage, those virtues are no protection against high-velocity weapons and air power. That's why they have returned to tactics which are a mixture of terrorism and guerrilla warfare and that's why the brigadier, the ambassador and the defence secretary were right to voice their concerns.

It now seems all too possible that Afghanistan could become a war without limits and that it could quite easily equal Operation Banner, the British Army's deployment in Northern Ireland between 1969 and 2007. No-one wants that. It would be time-consuming and become increasingly unpopular not just within Nato but also in Afghanistan itself. And it might soon become fiscally impossible to bail out the banks at home while propping up Afghanistan away from home.

This is not a policy of despair. Far from it, I have always maintained that Afghanistan is not a lost cause but a cause that is waiting to be won. And it is eminently winnable if the correct approach is taken. In common with every other counter-insurgency war that was ever fought, there has to be a political dimension to the campaign and that's why it's good to hear that lines of communication have been opened with the Taliban. For the past fortnight, in conditions of utmost secrecy, Afghan negotiators led by Qayum Karzai, brother of the Afghan president, Hamid Karzai, have been in Saudi Arabia where they have been talking to their Taliban counterparts.

Already the discussions have borne some fruit, with the Taliban agreeing to end indiscriminate attacks on humanitarian aid convoys and to give some consideration to the possibility of breaking off their links with al-Qaeda terrorist groups. Small though those concessions are, they do represent a breakthrough of sorts. With presidential elections due next year it would be better to have the Taliban inside the big tent than causing mayhem outside it.

However, there is still a long way to go before discussion can take the place of guns. Soldiers like Carleton-Smith know only too well that the Taliban are not exactly known for adhering to pacts which don't suit them. His predecessor in Helmand, Brigadier Andrew Mackay, had to retake the town of Musa Qaleh after it had been handed over to local elders only for the Taliban to renege on the agreement. Cue the return of the insurgents followed by a bitterly fought battle by 52 Infantry Brigade to kick them out once again.

While the talks are continuing it makes sense to keep up the military pressure for the simple reason that the mainly Pushtun Taliban understand the vocabulary of violence. They have managed to consolidate their position, too, winning control of provinces including Ghazni and Wardak where de facto alternative governments have been established. Here they have been helped by the corruption and feebleness of Karzai's government and by their own ability to instil fear in the local population.

Only one thing prevents the whole house of cards from collapsing: some of the younger Taliban warlords seem to have come to the conclusion that Nato is in Afghanistan for the long haul and that its armed forces are unlikely to throw in the towel. Slowly, the infrastructure is being constructed and there is little likelihood of withdrawal until good governance and a sizeable measure of stability have been restored.

It's an old story and it lies at the heart of the solution to any vicious counter-insurgency war: keep hitting the unreconstructed fighters with a big stick and start waving the carrot at the more discerning moderates.