A leading Western authority on Afghanistan says that the war in Afghanistan cannot be won militarily and that the current regime headed by President Hamid Karazai is not strong enough or secure enough to govern its own territory without a political settlement.

The author of such strongly felt, if realistic sentiments, is Sir Sherard Cowper-Coles, Britain's former ambassador in Kabul and, until recently, the UK Foreign Secretary's Special representative for Afghanistan and Pakistan.

In an exclusive interview, Sir Sherard amplifies what he argues in his newly published book, 'Cables From Kabul', namely that "Even if our military achieves local, tactical and temporary success in Helmand or Kandahar, that will be far from enough to achieve within three years our wider strategic goal of stabilising Afghanistan to the point where the Afghan authorities can secure and govern the country with only money and advice from outside."

Sir Sherard's views have attracted attention on both sides of the Atlantic because his book was published a good month before President Barack Obama announced his intention of withdrawing some 30,000 US troops from Afghanistan by the end of 2012.

By doing so, the US President is effectively endorsing Sir Sherard's conviction that the only way ahead is to recognise and deal with realities on the ground. In effect this means talking to the Taliban, something the Americans have been doing in secret for several months with representatives of Mullah Omar.

Sir Sherard's own interesting take on the Taliban is that "the best way of protecting the women of Afghanistan and others is by negotiating the Taliban into a settlement. If we don't, they will in all probability take over great areas of the South and East and turn those areas into a new Dark Age.

We've already seen that with the executions and punishments being meted out in areas of Afghanistan which the Taliban control, despite the Afghan government.

"The other thing we need to lock in is signs that the Taliban themselves are divided with any growing and large tendency among them to recognise that they went too far the last time they were in power and that next time round they have to be more connected with the real world, more connected with the modern world, allow women to be educated and to work. They will allow people to watch television and listen to music the next time, which they didn't the first time round.

"The Taliban themselves are evolving and we need to capture that and encourage that tendency by engaging them and not by trying to isolate and suppress them. Of course there will always be some who will reject any deal and those do need to be isolated. But with luck they should be a tiny and containable minority. As with any insurgent movement of this kind there are always some rejectionists.

Any future deal with the Taliban risks wiping out the political gains that India hoped to consolidate with its massive programme of social and economic aid to Afghanistan, including investments in schools, transport and power infrastructure.

However, everything would not be lost for New Delhi if Cowper-Coles' strategy for Afghanistan's future is embraced by all interested parties. He says that any future settlement can only succeed if it is guaranteed by the international community, including India as the regional super power.

"You know we have to recognise that Pakistan has a large and legitimate interest in Afghanistan. So does India as the regional superpower. India needs to be part of the solution in Afghanistan. China, Russia, Iran, Saudi Arabia, Turkey, the three 'stans, they all need to be there."