Aspiring Isis recruits are more likely to be better educated than their compatriots, a new study from the World Bank based on leaked internal documents from the terror group has found.

The socio-economic study, aimed at trying to understand the pull factors of Isis' particular brand of extremism, found that more than a quarter of foreign recruits had a university level education, and only 15 per cent of the 3,803 case studies had not finished secondary school. Only two per cent were illiterate, debunking the theory that poverty and level of education are linked to radicalisation, the report said.

Breaking down the data according to geography suggested that on average, Isis recruits are young, single, with low access to resources or employment with which to start a family, and have a “slightly more than basic” understanding of Islam, even if they are well educated.

Would-be suicide bombers were mostly likely to have experienced unemployment or have military experience, and were also the wealthiest of foreign recruits.

The self-volunteered data collected from the joining papers of almost 4,000 fighters from Europe and the Middle East dates from early 2013 - late 2014, and was leaked by a former member of the group who defected in March this year. It is thought to betray details of approximately ten per cent of Isis’ total fighters.

Recruits listed their nationality, education, ages, former occupations, and which roles they wished to be considered for in Isis’ so-called caliphate across Syria and Iraq. The average age of a fighter is 27, with the youngest on average coming from Libya (23) and the oldest from Indonesia (33).

In pictures: Civilians freed from Isis in Manbij Show all 11 1 /11 In pictures: Civilians freed from Isis in Manbij In pictures: Civilians freed from Isis in Manbij Women and children celebrating after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A man cuts the beard of a civilian who was freed from Isis by the SDF in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Women carry newborn babies while running after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman freed from Isis hugs an SDF fighter in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman adding her veil to a pile of niqabs burning in Manbij, Syria, after being freed from Isis on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Children celebrating on top of a lorry after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A man and child freed from Isis by the SDF in Manbij on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman carrying her children walks towards SDF fighters after being freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij A woman and child freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij An SDF fighter kisses a crying man who was freed from Isis in Manbij, Syria, on 12 August Reuters In pictures: Civilians freed from Isis in Manbij Hundreds of civilians freed from Isis in Manbij, Syria, on 12 August Reuters

Earlier this year, the New America Foundation, a political think tank, dug into the same data to discover what localised factors drive foreigners to join the caliphate, finding people join the group for lots of different reasons, and at different stages in their lives, depending on where they're from.

Derna in Libya, where interest in Isis was strongest, is a very poor area with a long history of Islamist resistance to the state, whereas fighters also came from Quassim, a Wahabi heartland in Saudi Arabia, which is highly educated and relatively wealthy.

Isis has faced a string of military defeats across its territory this year. Author Nate Rosenblatt said as more and more people try to defect, the fight against the group may change to a battle against fighters who return home and continue the ideological battle from there.