'Hundreds' of British fighters remain in IS ranks: defector

As the Islamic State group comes under siege in Iraq and Syria as many as 300 British nationals may still be fighting with the extremist group, according to a recent defector, currently in Turkish police custody.

Stefan Aristidou, 23, from Enfield was arrested in the Turkish border town of Kilis, last week. 

Before crossing from Syria into Turkey Aristidou spoke to The Telegraph through an intermediary. 

He said that "somewhere between 250-300" British IS fighters remained, most operating in Syria, many "in higher roles".

Aristidou, a convert to Islam, left the UK in April 2015 with his girlfriend, also a British national. He has claimed that he travelled to Syria to live under Sharia law, rather than to fight for IS. 

It is unclear whether he will be tried in the UK or in Turkey. 

Between 850-1,000 British nationals are estimated to have left the UK to join IS and other jihadist groups. Around half have returned to the UK, while more than 100 are thought to have been killed. 

British security officials have said that returning fighters could pose a "huge challenge" and are on high alert following the expected defeat of IS in its strongholds of Mosul, in Iraq, and Raqqa, in Syria. 

An exodus of foreign fighters from these cities is already thought to be underway. 

In March The Guardian reported that British security officials had established procedures to manage the return of fighters to the UK, in particular working in cooperation with Turkey, a main transit point in and out of Syria. 

Such cooperation has been cited as one reason for the UK's muted criticism of growing authoritarian practices exercised by President Recep Tayyip Erdogan.