Are we getting into bed with the devil?

But, while President Bush and Tony Blair may be anticipating a celebration, for those who know the Northern Alliance, the response is more muted.

Even among the ranks of the US-led coalition, there is caution over how far to take support for the disparate group of warlords who make up the Northern Alliance. The Alliance itself has apparently agreed not to try and take Kabul, but instead to wait until efforts to build a broad-based new government for Afghanistan bear fruit.

But even if Alliance commanders can restrain their troops, euphoric after a startling series of successes and in the face of Taliban retreats, there is a growing disquiet over the West's use of a proxy army, which may turn out to cause as many problems as it solves. Along with its human rights record, at least as horrific as the Taliban's, a Northern Alliance government also brings the prospect of sustained conflict between Afghanistan's rival ethnic groups, as well as further destabilising the entire region.

"The Americans don't want them to enter Kabul because they want to keep their alliance with Pakistan," says David Campbell, professor of international politics at Newcastle University. "Pakistan traditionally backed the Taliban, whereas the Northern Alliance is backed by India and Russia. Pakistan is unlikely to want to see allies of India and Russia in control right next door.

"The Northern Alliance is a very loose alliance of warlord groupings, who have an extremely unsavoury human rights record. It is responsible for all sorts of human rights abuses, including fairly large-scale massacres of civilian populations. Most of those fighting within Afghanistan over the past 23 years have a pretty poor human rights record. These guys are no saints."

Campaign group Human Rights Watch has raised its own concerns over the Northern Alliance, also known as the United Front. Its catalogue of abuses include summary executions and looting and burning of houses in the Sangcharak district, while it was under Alliance control for four months in late 1999 and early 2000; rocket attacks on a crowded market in Kabul in September 1998; the execution of 3,000 captured Taliban soldiers in May 1997 and widespread looting and rape in Kabul in 1995 by one of the factions that went on to form the Alliance. It is no surprise that few ordinary Afghan civilians relish the prospect of the Alliance taking power.

The Alliance was created in 1996, when the Taliban captured Kabul, and supports the ousted government, the Islamic State of Afghanistan (ISA). Former president Burhanuddin Rabbani is the titular head of the United Front, although the real power was in the hands of Ahmed Shah Massoud, the ISA's defence minister and a legendary commander, until his assassination just days before the September 11 terrorist attacks. The United Front is predominantly made up of Tajiks and Uzbeks, as opposed to the Pashtun-dominated Taliban, and encompasses groups including Jamiat-i Islami, Hizb-i Wahdat and Junbish.

"These groups initially grew out of opposition to the Soviet Union in the 1980s, and then came together to oppose the Taliban," says Professor Campbell. "From the Americans' point of view, they have no alternative, because the Alliance is the Taliban's opposition, but it is a huge, huge gamble.

"The Americans are trying to collapse the Taliban and put in place a political alternative, of which the Northern Alliance will be a part, but they don't want it to be the only one. They want to construct a broad-based, ethnically-diverse political grouping."

The Russians are supplying the bulk of the Alliance's equipment, although US special forces are working with them. But if the Taliban regime is ousted, these weapons will still be in the hands of Alliance troops. "It is such a dangerous game to play," says Professor Campbell.

"We have so quickly gone from a war on terrorism, to opposition to the Taliban, to overthrow and setting up a new administration in Afghanistan. The jury is still out on whether that is going to have any positive impact against so-called terrorism. As much as George Bush and Tony Blair say they don't wish to be involved in nation-building, it is hard to say that is not what they're doing." The Northern Alliance is also viewed with fear and suspicion by the majority Pashtun population of Afghanistan, who largely occupy the southern half of the country. And support for the Alliance is largely confined to the north, according to Pat Chilton, professor of international relations at Sunderland University.

"It is not just a group of all the people who oppose the Taliban," she says. "In my reading, their raison d'tre isn't so much opposing the Taliban, as trying to protect their own fiefdoms and prioritising their own tribal and regional loyalties.

"The falling out between groups, largely on regional and ethnic lines, took place after the Russians went, but also the Western support was withdrawn, leaving them fighting each other, which is typically what happens in a post-external involvement situation. The Alliance is in no way a reasoned ideological opposition to the Taliban."

But using the Northern Alliance to carry out the West's dirty work is likely to come at a price. And there is an instructive parallel in Kosovo, where the West supported the KLA, supplying it with weapons and setting up fighting divisions, only to see the conflict prolonged once the West's targets had been achieved, and also to see it spreading into neighbouring Albania and Macedonia.

"It is a classic follow on of what happens after you supply a local army to do your dirty work," says Prof Chilton. "That is also how the Taliban came to be there: we were using them to do our dirty work. We are talking about bit players who happen to be not the Taliban, and using them to push the Taliban out.

'Nobody is arguing seriously that they want the Northern Alliance in power, but it is going to be very difficult to extract a long-term success from this position." The immediate problem, she says, is keeping the Alliance out of Kabul, or stopping them from massacring the majority Pashtun population if they do take the Afghan capital. But there is also the long-term future of the country to consider.

"The longer-term problem is how the Western coalition controls what happens, not just in the next few weeks and months, but in the months and years following. How the coalition will try and create something different from what was created 15 or 20 years ago from fighting the Soviets.

"There is far too much glossing over this problem, and pretending that it isn't a major problem, but it is. They are saying they will cross that bridge when they come to it, but, historically, when it gets to that stage it is nearly always too late."