UK nationals travelling overseas to serve with extremist groups as "foreign fighters" present a potential threat to the UK, both while they are overseas and when they return to the UK.
While overseas, these fighters can help terrorist groups to develop the ability to carry out attacks by linking them up with extremist networks in the UK and providing information about potential targets. In addition to English language skills, which can help these groups reach a wide audience through propaganda on the Internet, some foreign fighters may also have other specialist skills (e.g. scientific, IT) that can be useful to overseas terrorist groups.
Foreign fighters can gain combat experience, access to training and a network of overseas extremist contacts. The skills, contacts and status acquired overseas can make these individuals a much greater threat when they return to the UK, even if they have not been tasked directly to carry out an attack on their return. Experience of fighting overseas with terrorist groups can also promote radicalisation.
Syria is a particularly attractive destination for UK extremists wishing to engage in violent jihad. Hundreds of British extremists have travelled there, a significant proportion of whom joined the Islamic State of Iraq and the Levant (ISIL). The nature of the conflict in Syria and presence of ISIL and Al Qaida-affiliated groups such as the Al Nusra Front (ANF) make the country a significant source of threat to the UK and UK interests overseas. We have also seen British nationals travel to Pakistan, Yemen and Somalia to fight or obtain terrorist training.