Behind the glinting ribbons of freshly strung barbed wire, the 100 beds at the new high-security drugs wing of Pul-e-Charki prison on the outskirts of Kabul stand empty. Who fills the two-person cells over the coming months will provide one quiet indication of whether the war in Afghanistan – on drugs and against the insurrectionist Taliban – can be won.

General Shah Mir Amirpoor, the prison director, boasts that the $2m block – funded in part by the United Nations – is so heavily fortified that the inmates “won’t be able to escape, even by helicopter”.