There was little to draw foreign visitors to the town of Manbij in northern Syria before the civil war. It had not much more than a post office, a prison and a large flour mill.

When Isis (Islamic State) took over, however, this unremarkable town became a meeting place for jihadis from around the world.

Most of all, it drew British fighters. So much so, it has now become known as "Little London". Half an hour's drive from the border with Turkey, Manbij is the first stop for fighters arriving from Europe and has become the front line of the holy war for a caliphate.

As many as 100 Britons are living in Manbij, residents have told the Daily Telegraph. An estimated 700 are thought to have travelled to Syria to fight since 2011, half of whom have since returned to Britain.

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"There are about 30 nationalities of ... fighters here: Britons are the highest, then the Germans and the French, then the Saudis and the Algerians," said Husain Khalaf, an activist living in Manbij. "It has the most Europeans of any town in Syria - now Arabic has almost become the second language."

Last week, one of its youngest British residents became the unwitting star of an Isis propaganda video, which showed the execution of five men accused of being spies.

Four-year-old Isa Dare - who was taken by his mother, Khadijah, from London to Manbij - was seen threatening the "infidels" in the West.

Western fighters with young families are sent to Manbij rather than the group's de facto capital of Raqqa, 130km further east, because the town is considered safer - largely spared from regime and coalition airstrikes.

Isis has strict and unchallenged rule over the town, which has a population of around 150,000. Women must cover their hands and face and must not mix with men in public; Western clothes are banned, so are music and smoking.

A video released by the terror group ISIS shows a young boy coldly executing two men who the terror group claims were Russian spies. Photo / Supplied
A video released by the terror group ISIS shows a young boy coldly executing two men who the terror group claims were Russian spies. Photo / Supplied

A former resident who used the pseudonym Ali Al-Khatib told the

Telegraph

: "The British are the most brutal."

Khadijah Dare, whose own husband died last year fighting, has lived for the last 18 months in the town with Isa and her younger son.

Leaked Isis documents have shown that the brainwashing of children and the use of child soldiers is key to the group's consolidation of its "state".

At the age of 10, children in Manbij are enlisted in "cubs of the caliphate" training camps. They are taught how to fight, use weapons, behead captives, deal with prisoners - and even how to carry out suicide missions.

- Telegraph Group Ltd