Mohammed el-Araj, 23, from West London, left, died in August during an ambush on Assad forces

Britons make up the majority of foreign fighters in the most violent terrorist group in Syria, blamed for beheadings and crucifixions, a senior Syrian rebel commander has said.

Brigadier-General Abdulellah al-Basheer pleaded with Britain to send weapons to the moderate but outgunned Syrian opposition to help them to deal with the increasingly brutal threat of the Islamic State of Iraq and al-Sham (ISIS).

In a letter to The Times he warned that a failure to act could lead to British extremists returning home to “continue on their pernicious path of destruction”.

The warning, from a leading member of the Free Syrian Army, came as MPs said that a debate on policy in Syria was long overdue, particularly given the threat posed by returning jihadists. “That