MORE than 500 British Islamic extremists are planning terror strikes in the UK, according to secret figures obtained by the Daily Mirror.

Some of the jihadists, who are being watched by MI5 and counter-terror police, have already obtained bomb-making materials.

The figure, which fluctuates between 450 and 550, represents the number of monthly live investigations carried out by undercover spooks at any one time.

A counter-terror source said: “Make no mistake these people represent extremely serious threats to UK citizens – the threat of a mass atrocity committed against the public is real.

“Some of them not only have the intent but the material needed to carry out that intent and they represent the most serious threat.”

Some would-be terrorists under surveillance are potential “lone wolf” bombers. These are the most difficult to monitor because they do not talk about their plans.