However, M15 whistleblower David Shayler (right) got worryingly carried away when he took part in a schools Question Time debate at City and Islington sixth form college.

Asked by a student about US policy in the Middle East, he broke into a rant in which he attacked “the Zionist bankers controlling the world”. This was met with an enthusiastic round of applause.

He then launched into classic conspiracy theory territory, with his view that there was no evidence to support the contention that the September 11 attacks were caused by external forces. This was also applauded.

“I used to work for MI5, so I know what I’m talking about,” Mr Shayler said.

A solitary pupil questioned whether “Zionism” was being used as a euphemism for “Jewish”. Mr Shayler was outraged at the slur on his character: “Would you deny that the Zionist bankers, the Rothschilds, are working for a greater Israel?” he frothed.

We hope pupils at City and Islington college have a chance to examine some of Mr Shayler’s other beliefs, perhaps as part of citizenship. His theory that the planes which thousands of people witnessed flying into the World Trade Centre were actually missiles surrounded by holograms could also make for an interesting physics class.