It was early 2006, and the paratroopers of 16 Air Assault Brigade took a breather during exercises on Salisbury Plain to say what they had been told to say about their forthcoming campaign in Helmand province. “Reconstruction, reconstruction, reconstruction,” they piped in unison.

Three years later the politics of this campaign have changed beyond recognition. Instead of reconstruction, we have had violence and mayhem, and the public in Britain, in the United States and in every country that has troops in Afghanistan are asking what has gone wrong, and if lives are being sacrificed needlessly.

The biggest challenge for the Government now is not how to beat the Taleban but how to keep the public at home onside. People tend to support the Armed Forces whatever they do but if there is any perception that British troops are dying in Afghanistan for no good reason the tide of opinion will turn.

It is difficult to get across the message that Britain is at war. There are no daily bulletins from the Ministry of Defence, as there were when a Royal Navy Task Force was sent off to the Falklands in 1982. But the “Wootton Bassett factor” — the Wiltshire town where mourning crowds gather whenever a hearse carrying a dead soldier passes through — is having an effect on the nation’s psyche.

Other Nato countries have the same problem. In Italy, for example, the mission in Afghanistan is normally described as a peacekeeping operation. Then six Italian soldiers are killed by a suicide bomber, and suddenly it’s a war, and Silvio Berlusconi, the Prime Minister, tells his public that he wants his troops out.

Germany was the forgotten ally, with its troops engaged in non-combat roles in the north until the Taleban began to move in and upset the peace. German soldiers died and the soft rules of engagement had to be changed to allow them to shoot first and ask questions later. Back home in Germany the “war” was suddenly no longer an issue just for the British, Americans, Canadians, Dutch, Danish and Estonians, engaged in daily skirmishes with the Taleban in the south. It was a shock for the German public and for the Berlin Government.

No government can afford to forget the power of public opinion. Despite the mantra that the troops are being sacrificed in Helmand to prevent terrorist attacks on our streets, the argument is difficult to grasp when even the head of MI5 admits that the majority of the terrorist incidents in this country can be linked back to Pakistan — not to Afghanistan.

Nevertheless, the argument is sound. Afghanistan has to be seen in the context of the region, not as a country in isolation. If the Taleban were allowed to dominate Afghanistan, there are enough links with their fellow fanatics in Pakistan — in the Taleban and in al-Qaeda — for the nightmare scenario to develop: jihadist extremists with their hands on nuclear weapons. British troops are not being sacrificed in vain.

At present there is no sense that the public want the troops to be withdrawn. A recent Populus poll for The Times, however, indicated a growing desire for some form of timetable to be set. Ministers and military have begun to opine about maintaining a combat role for three to five years in Afghanistan before handing over to the Afghan security forces. This might not seem achievable today but it is not unrealistic.

Bob Ainsworth, the Defence Secretary, told The Times yesterday: “Back home the Government has to make clear the real reason why we need to be in Afghanistan. First and foremost, we must get security right so that we can prevent Afghanistan from once again becoming a haven for terrorism. Building the Afghan state — its education and health services, alternative livelihoods to drugs and a strong legal system — will give the people a better future than the one offered by the Taleban.”

Three years into the war in Helmand, now is not the time for a loss of nerve on the part of either the Government or the public.

The Americans have only recently begun to focus their efforts on Afghanistan, after the comparative success of the surge in Iraq, and General Stanley McChrystal, the US commander, needs time and support to implement a proper military strategy.

Every example of nervousness aired in the public domain provides the Taleban with a psychological boost. Psychology in war is just as important as military muscle; the will to fight comes not from a commander’s edict but from a belief that victory is possible.

British troops in Helmand want to win — but if they hear that public support is wavering back home, morale on the front line could be seriously affected. To judge by reports coming out of the capitals of the Nato countries with significant troop contributions in Afghanistan, there is plenty for the Taleban to smile about, not least from the extraordinary dithering now in evidence from President Obama and his closest advisers.

Mr Obama knows that Afghanistan is now “his” war — just as Iraq was President George W. Bush’s war — but already the foundations for his ambitions to succeed are crumbling.

Senior Democrats have voiced their opposition to sending more US troops, and now we hear from Washington that the President himself, plus Joe Biden, the Vice-President, and Hillary Clinton, the Secretary of State, are getting cold feet about General McChrystal’s call for more troops. The general must be sitting in his office in Kabul with his head in his hands.

Gordon Brown is also under pressure to make up his mind about troop numbers. The military is arguing for another 1,000 to help to hold ground seized from the Taleban — taking numbers to almost 10,000 — but the Prime Minister has to weigh up whether the public will back more reinforcements at a time when casualties appear to be rising remorselessly.

The same debate is going on in the rest of Nato.

It will not take long before growing doubts within the alliance begin to have an effect on public opinion, unless a bit more backbone is shown by Nato leaders.

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