Michael Portillo, whom is usually a fool, makes some very good points about the war in Afghanistan here. Unlike Iraq, the Afghanistan war was not a war of choice because the Taliban were in symbiotic relationship with Al Qaeda who were responsible for the murder of thousands of civilians, including a couple of hundred Britons. Unfortunately the resolve to pacify Afghanistan that existed after the 9/11 attacks has largely evaporated, particularly so among many members of Nato.
Britain's government has left the armed forces underfunded which is shameful considering the sacrifices that are being demanded of them, but Gordon Brown has preferred to use the gargantuan increases in taxation to fund his personal follies such as the failed 'New Deal' scheme or to throw money at Labour voting areas. In short the government has consistently used the armed forces for various global vanity projects that will garner the government popularity, but refuses to fund the MOD is order to appease the pacifist leanings of many of their own backbenchers.
However Britain is at least meeting the commitments to keep the Taliban out of Afghanistan, and the army has been engaged in serious fighting, with all the losses that are entailed. Meanwhile other members of what is supposedly an alliance, are shirking their duties entirely or in part. Germany for example has troops in Afghanistan, and Angela Merkel has been resolute in refusing to be intimidated into leaving, but their soldiers are based in and around Kabul which is where the fighting isn't. Peace keeping is considered to be something distinct from fighting the groups that are threatening to destroy the peace. France, Spain, Italy and Turkey are all among the countries which have refused to commit more troops. Turkey aside most of the absentees are staying away purely for domestic political advantage, however short term that turns out to be.
Afghanistan has not been an easy place to win a war historically, and NATO is doing much better than other outside powers, but at the moment the strain of the struggle falls on a handful of members. The others need to be cajoled, persuaded and prodded into engaging fully. Germany for example wants to be a permanent member of the UN Security Council, the UK ought to make it clear that it cannot support the membership of a country that is unwilling to fight. Most of the members of NATO are also members of the EU, and thus receive money indirectly from the UK, that is another lever of power to be exploited.