This was the justification for keeping the border at least partly open. The problem is that the US, Britain, Turkey, Saudi Arabia and others have pretended that they are backing a powerful non-jihadi opposition movement capable of displacing Assad. Over the past year, Turkey has done something, but not nearly enough to close the border to jihadis. Those who head for Iraq must also take what Turkish journalists call 'the Jihadist Highway', a network of roads across Turkey and Syria.

The Turks have a 560-mile border with Syria and it is across this that jihadis must travel if they are to reach their destination, primarily but not exclusively the Islamic State of Iraq and the Levant (Isis), to offer their services. The point at which jihadis should be best identified, intercepted and stopped is not within Britain or even Europe, but as they cross from Turkey into Syria.

The discussion, driven by politicians responding to media hysteria, produces a sort of intellectual fog in which effective measures that can be taken swiftly disappear from view. Much of what is said is irrelevant to the real circumstances in which Muslims leave Britain or other foreign countries to fight in Syria and Iraq. Dubious counter-terrorism specialists, the exact nature of their expertise frequently elusive, speak of the effectiveness of new controls in thwarting actual or potential jihadis. The murder of the US journalist James Foley by a British jihadi has reignited the barren debate in Britain about new government powers to tackle extremist Islamic groups.

Borderlands splinter group puzzle