Leading article: From liberators to occupiers?

The death of another British soldier in Afghanistan - the 61st to be killed since this nation first sent forces there in 2001 - is a reminder of just how dangerous and costly our commitment has become. The country that saw a series of bloody and disastrous British invasions in the 19th century is now absorbing Britain's largest single military deployment abroad - a total of 7,000 troops, compared with 5,000 in Iraq.

It is a deployment, it has to be said, that has grown exponentially, without there ever being a proper definition of war aims, let alone a full account to Parliament and the people. The original purposes of the engagement were clear enough: to support the United States in a multinational campaign to remove a regime which had harboured the 9/11 plotters, and effect their capture.

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Nearly five years later, Britain finds itself with an entirely different role of supporting a shaky government, rooting out the burgeoning drugs trade and leading a major Nato deployment in the south of the country against a resurgent Taliban force. It is a task which, according to our ambassador in Kabul, Sir Sherard Cowper-Coles, could last a "very long time" - as much as 30 years, indeed.

Quite aside from the fact that there is no parliamentary sanction for this kind of commitment - and the British ambassador is hardly in a position to make such a promise by himself - there is a serious question of whether it is wise or even practical. The professionalism and courage of the British troops on the ground are not in doubt. They have thrown themselves into a difficult and continuous engagement with Taliban forces and, on the basis of such information as we have, have achieved their main task of stopping a much-forecast Taliban summer assault.

But with the passage of time their role has become increasingly that of supporting not so much democracy as such but of the particular regime of President Karzai, a leader who has so far failed to impress as a national president or to put himself above tribal loyalties. Without intending to, the British and other western forces risk being seen not as liberators but occupiers, a position only reinforced by their task of rooting out the opium crops on which many Afghans depend for their livelihood. Nor has their popularity been increased by the ratcheting up of a Nato bombing campaign against the Taliban that has seen hundreds of civilians killed.

When you're in a hole, stop digging, Denis Healey famously advised his fellow politicians. It could be said of Afghanistan now. It is time to review the nature of our commitment. The change at Number 10 offers the perfect opportunity to do so.