In Afghanistan, the recent deal between the Brits and local tribal leaders in the Musa Qala district, under which the British agreed to pull out, if a tribal police force was formed to provide security, is one of several such agreements that have been made recently. Afghan president Karzai has apparently been pushing for this sort of deal for a while, but US commanders were reluctant to use it. Fact is, U.S. commanders have tried these deals, but there have been embarrassing incidents as a result. The tribesmen will take bribes from Taliban or al Qaeda, and often do it at times when their American paymasters really don't want to see that sort of thing happening.
The Brits, with their long history of dealing with tribes in this region, have been using this sort of thing for centuries, and appear OK with the quirks that drive the Yanks nuts. Of course all deals with tribes are essentially transitory, and will have to be renewed from time to time. Moreover, if the Brits get burned like the Americans have (as in some al Qaeda fellows bribing their way past tribesmen the British thought they had a deal with), than these arrangements won't seem so "sensible." Indeed, an important difference between these arrangements now, and in the past, is that earlier deals were usually about keeping the tribes from raiding into British controlled territory. This time around, the British troops are in tribal territory, presenting the unruly elements in the tribes with much, perhaps too much, temptation.