Leading article: The bloody cost of spying

If the revelation that the suicide killer of seven CIA officers in Afghanistan was a double-agent for al-Qa'ida sounds like the plot of a Le Carré novel, that's because that is exactly what it is. This is the murky world of turned terrorists, secret meetings and bloody double-crosses which has been the subject of many spy novels. The question is whether the game being played here was a worthwhile exercise or a diversion from the real job of building up knowledge of the world in which Nato forces are operating.

The head of military intelligence in Afghanistan, Major General Michael Flynn, clearly thinks the latter. In a damning new report he paints a devastating picture of an American intelligence effort so concentrated on specific threats such as roadside bombs that it is unable to offer anything on the broader political and social background to the war.

At the heart of this issue is the increasing role that has been played in American tactics by unmanned drones to assassinate al-Qa'ida and Taliban leaders. Such a policy demands precise knowledge of targets that is best delivered with the use of ground intelligence as well as aerial surveillance. Hence the trap the CIA fell into by trusting, according to reports in Washington, a Jordanian former terrorist whom they believed they had turned and allowing him into the compound unsearched.

That they trusted too much is a reflection of the pressure they were under as much as their own competence. But it should also raise more fundamental questions about the policy of targetted assassinations from the air, which all too often inflicts heavy civilian casualties and turns the local population against the "foreigner" firing from the skies.

The pursuit of human intelligence will always involve risk. In the broader picture, however, Maj-Gen Flynn is surely right. The best intelligence comes from a steady process of gathering a picture of the environment, not pursuing James Bond-style adventures. If this violent setback to the CIA leads Washington to even more reliance on aerial surveillance and drone attacks, it can only be at the cost of local support for its – and our – presence in the country.