The Trident nuclear submarine system is at the centre of a political fight over whether the UK maintains its own deterrent or spends the money elsewhere

Standing in a tent in a British army base in Afghanistan, Lieutenant Colonel Steve Crouden looks at a map of Helmand province. “This area here is pretty much the same size as west Belfast,” says the military planner, pointing to a well-populated town. “Back in the old days, at the height of the Troubles in Northern Ireland, we would have had two or three thousand men patrolling an area like that. But in that town in Afghanistan we’re doing a similar job with only a few hundred. It says a great deal. We’re stretched, we’re under pressure.”