MI5 fear that militant Islamists will attempt to exact revenge on the British spy, who penetrated al-Qaeda in the Arabian Peninsular (AQAP), by publishing his photograph on the internet – a move designed to incite extremists to hunt him down.

Sources have described the British spy as “gold dust”, adding that he was one of just a handful of agents in the last ten years to have successfully penetrated one of the groups aligned to al-Qaeda’s concept of global Jihad…

It us unclear whether the man’s radical roots were genuine, and whether he infiltrated AQAP as a mole or only changed sides later.

AQAP knew that Saudi intelligence agencies, who “handled” the agent, were trying to infiltrate the group so they would have conducted detailed checks on the foreign volunteer, helped by sympathisers in Britain.