Jihadists in Syria have hacked into British ministerial email accounts in a sophisticated espionage operation, the Telegraph disclosed Saturday.

An investigation by the intelligence agency has discovered that extremists linked to the Daesh group have been targeting information held by some of David Cameron's most senior ministers, including Theresa May, the Home Secretary.

It is understood that at least one of the plot's ringleaders was killed by a drone strike in an operation disclosed by the Prime Minister this week.

By hacking into the private offices of senior ministers, the extremists could have discovered events that government figures and members of the Royal family were expected to attend.

The Telegraph learned of the operation several months ago, but agreed not to publish while the investigation continued.

On Monday, it emerged that a British jihadist had been killed in Syria by UK forces after he directed a plot to kill the Queen.

The Prime Minister said it was the first time Britain's Forces had directed an attack against one of its own citizens while not at war.

Reyaad Khan, 21, a Daesh fighter from Cardiff, was killed by a drone operated from Lincolnshire.

A second Briton, Junaid Hussain, a computer hacker from Birmingham, was killed by US forces three days after the British strike.

Hussain, who joined Daesh in 2013, with Sally Jones, 46, his Muslim convert wife, is thought to have been involved in the cyber attack.

It is unclear what information the extremists were able to access, but it is understood that no security breaches occurred. However, officials were told to tighten security procedures, including changing passwords.

The disclosure shows how the so-called "war on terror" has developed because of Daesh's cyber capabilities – computer hackers are known to have been recruited by the group to "actively target the West".