Actually not quite true.
The Brits were unwilling to pay the price to conquer and occupy Afghanistan, if they indeed were capable of doing so.
Instead, they established a "buffer zone" in their NW Provinces. These areas are largely occupied by Pathans and other peoples who are "really" Afghans. The Brits didn't try to control this area. They paid off local chiefs to keep the level of violence to a dull background roar. They would make punitive expeditions every few years to keep the inhabitants from getting too out of hand.
It was essentially a policy of "whack a mole" as has been proposed. "Rubble doesn't make trouble" wouldn't work because there wasn't much there but rubble to begin with.
The Brits also fought several real wars with the Afghans themselves, the last in the 1920s.
But the Frontier was never quiet, and raiding never stopped.
I stand corrected; We’ll have to go with the Mongol method.