Mission impossible? Is the British Army being asked to fight a battle too far in Afghanistan?

Soldiers will have to tackle security, reconstruction and the drugs trade. By Raymond Whitaker and Justin Huggler

A wave of violence has hit the region of southern Afghanistan where British troops will soon be deployed, with two policemen killed by a roadside bomb and three newly built schools set on fire in the past week.

The Secretary of State for Defence, John Reid, announced on Thursday that 3,300 British troops will be sent to Afghanistan's Helmand province in one of the most complex and delicate missions the British Army has ever undertaken. In Helmand, part of the Taliban's former heartland and one of the country's main opium poppy-growing areas, they will be expected to establish security, take part in reconstruction and fight the narcotics trade, which is controlled by warlords. About 90 per cent of the heroin on British streets comes from Afghanistan.

The attacks on Helmand schools show the strength of continuing support for the Taliban, which is violently opposed to mixed education. Last month gunmen dragged a teacher from his classroom and shot him at the gates of his school after he ignored warnings to stop teaching boys and girls together.

Until now, British forces in Afghanistan have been operating in Kabul and the north, where they have been largely welcomed by a local population that suffered repression under Taliban rule. But in the south they will be heading into a forgotten war. This month there has been a sustained new offensive by the Taliban, with suicide bombings an increasingly common tactic. American bases due to be taken over by the British-led force have come under full-scale attack.

In Kandahar, the Taliban's former headquarters, where Nato is taking over from US forces, at least 24 people were killed in co-ordinated suicide bombings earlier this month. Another bomb killed a senior Canadian diplomat, Welsh-born Glyn Berry, whose funeral was held at London's St Martin-in-the-Fields on Thursday. The next day, the Taliban attacked the police headquarters in Kandahar. Seven insurgents were killed.

Apart from concerns about the mission's multiple and possibly conflicting goals, military chiefs fear the deployment will stretch Britain's troop resources to the limit. Lack of security has prevented any reduction so far of the 8,500-strong British deployment in southern Iraq; the Foreign Secretary, Jack Straw, said at the World Economic Forum in Davos yesterday that Britain "hoped" to draw down forces outside Basra during the course of this year, but gave no further details.

General Sir Michael Rose, former commander of peacekeepers in Bosnia, said the Afghan mission was worthwhile and fulfilled a promise - "though rather belatedly" - not to forget the country. But he added: "It is going to be quite difficult to sustain both missions [Iraq and Afghanistan] for any length of time."

Critics believe the problems of pacifying southern Afghanistan and fighting the drugs trade have been hugely increased by the haste with which the Bush administration turned its attention to Iraq as soon as the Taliban was overthrown in 2001. A new book by James Risen, a national security reporter for The New York Times, says this not only allowed Osama bin Laden and the remnants of al-Qa'ida to escape, but left Afghanistan to become a "narco-state".

According to figures quoted by the aid agency Care, total income from the drugs trade for Afghan poppy farmers and opium traffickers between 2002 and 2004 was over $6.8bn, more than double international aid in the same period. The annual opium trade of $2.8bn is more than half as large as Afghanistan's legal economy. Much of the profit has found its way to forces hostile to the Kabul government and the foreign troops supporting it, with commanders noting that the insurgents have recently gained heavier and more up-to-date weaponry.

The British forces' mandate may pit them against farmers, for whom opium is far more profitable than any alternative crop. An aid conference in London this week will seek donations to compensate farmers who abandon poppy growing, but such schemes need years of commitment and are difficult to administer. In the rest of Afghanistan, where Britain already heads efforts to curb the trade, many farmers have complained that they gave up growing poppies after they were promised free seeds and other incentives. But the aid never arrived.

Reshuffle: Changes free US troops to fight in Iraq

The British deployment in Afghanistan is part of a major reshuffle in the "war on terror".

Britain is taking the leading role as Nato's International Security Assistance Force assumes responsibility for the whole country and steps up its forces from 9,000 to about 15,000. The United States will run down its forces in south-east Afghanistan, giving it more resources for Iraq.

An extra 3,300 British troops will join the 1,100 already in Afghanistan and 1,950 announced earlier. The mission will last three years and is expected to cost £1bn.

Also sending more troops to Afghanistan is Canada, with about half of a promised force of 2,000 already in place in Kandahar. But the Dutch government has delayed until February a decision on whether to send about 1,500 troops.

Xanthe Hinchey