We have just had a second intelligence failure on Iraq. The speed and extent of ISIS’s sweep into the country took the UK governnment by surprise. Whitehall was not alone in this. As I reveal in the magazine this week, when representatives of the US Joint Chiefs of Staff came to London recently, Iraq was way down their agenda.

What makes this intelligence failure so worrying is that we are relying on the security services to keep track of the 400-odd Britons who have gone to fight with ISIS in Syria and Iraq. Senior government figures believe that of those who have gone to Syria and then returned to the UK, the authorities have lost track of one in four of them. This reveals the sheer scale of the domestic threat that we face.

One of the major security challenges for Britain over the next few years will be how to keep track of these radicalised and, now experienced, individuals. The danger is, as the IRA used to boast, that they only need to get lucky once.

Tags: intelligence, Intelligence services, Iraq, Islamism, Militants, Security Service, security services, Syria, Terrorism, Terrorists