French intelligence sources told the Canard Enchaîné weekly newspaper that they are “confronted with a strategy of infiltration” by radical Islamists at Paris Charles de Gaulle Airport.

Saboteurs have attempted to inhibit pilots’ ability to monitor aircraft engines, and tried to disable emergency exit slides, the newspaper said.

One suspect, a French convert whose wife runs a Koranic school near Orly airport, fled to Yemen when he realised he was under surveillance.

Air France personnel found “Allahu akbar” scrawled on the fuel tanks of close to 40 aircraft. One pilot refused to fly a plane with the markings.

Inflight safety videos have been re-programmed to play first in Arabic, and the names “Israel” and “Morocco” were changed to “Gaza Strip” and “caliphate” in the Geovision system that enables passengers to follow the flight on their screen. A ground crew member refused to guide a plane piloted by a woman to its parking slot.

Relatively affluent

Information collected by Islamic State showed that 43.3 per cent of recruits completed secondary school, while 25.4 per cent attended university. Only 13.5 per cent stopped after primary school, and 1.3 per cent said they were illiterate.

Islamic State recruits from Africa, Asia and the Middle East were significantly more educated than their compatriots, the World Bank said. The majority had previously held jobs, though unemployment was often a factor in their decision to go to Syria.