The new study by IHS Jane’s, a defence consultancy, estimates there are around 10,000 jihadists – who would include foreign fighters – fighting for powerful factions linked to al-Qaeda.

Another 30,000 to 35,000 are hardline Islamists who share much of the outlook of the jihadists, but are focused purely on the Syrian war rather than a wider international struggle.

There are also at least a further 30,000 moderates belonging to groups that have an Islamic character, meaning only a small minority of the rebels are linked to secular or purely nationalist groups.

The stark assessment, to be published later this week, accords with the view of Western diplomats estimate that less than one third of the opposition forces are “palatable” to Britain, while American envoys put the figure even lower.