Interviewed on Sky just now, David Cameron toed a line somewhere in the middle of the two extremes. He seemed to reaffirm his commitment to a long-term conflict, saying that he didn't want to "put an explicit time limit on it," and - crucially - that "you have to spend what is necessary to get the job done." But he also added that we "should be seeing this in terms of years not decades".
As someone who agrees with the British involvement in Afghanistan - if not, always, the way it has been conducted - I was mostly encouraged by Cameron's message. But, politically speaking, it's easy to see how he could encounter tensions in government. His "years not decades" claim could already contradict the new head of the Army, David Richards, who recently said that the "whole process [in Afghanistan] might take as long as 30 to 40 years." While I expect some people would actually prefer to see things in terms of months rather than years.
One thing's for sure: setting the parameters for Britain's Afghan mission will be one of the hardest tests for the next government.