When Usman Khan put pen to paper from his cell at Belmarsh Prison seven years ago, he begged for the chance to “prove” he no longer harboured extremist Islamic views or posed a threat to the British public.

Insisting his conviction for being part of a terror cell that planned to bomb the London Stock Exchange stemmed from mere immaturity, he added: “Now I am much more mature and want to live my life as a good Muslim and also a good citizen of Britain.”

Khan’s letter pleading to join a Home Office “deradicalisation course” was the start of his plan to hoodwink the British authorities and ultimately commit terrorism on the streets of London.

A year earlier, the judge who sentenced him to a technically limitless jail term had no doubt Khan had embarked on a “serious, long term, venture in terrorism”.

In his sentencing notes, Mr Justice Wilkie singled him out from other extremists on trial because he was clearly a devious and scheming man dedicated to his hateful ideology.