Over 850 UK-linked individuals of national security concern travelled to engage with the conflict in Syria and Iraq. We estimate that over 15 percent of those who travelled have been killed in fighting in the region and just under half have returned to the UK. Anybody who does return will be investigated by the police to determine if they have committed criminal offences or pose a risk to national security. Those who travelled to, or remained in Syria or Iraq from 2014 are more likely to be a current national security concern than those who travelled and returned before then. While it would not be appropriate to provide a breakdown of the investigation status of travellers or returners, a significant proportion of those individuals who have already returned fall into the latter category and have been assessed as posing little or no national security concern.