The London Bridge ringleader was arrested by police earlier this year after he attacked an Islamic scholar - but he was let off with a caution.

Khuram Butt was reported to counter-terrorism officers following the incident but they concluded he did not pose a terrorist threat.

Butt launched a verbal and physical attack on Dr Usama Hasan, a senior member of staff with Quilliam, a think tank which counters Islamist extremism, at a festival in east London in July last year.

According to Quilliam, police finally tracked down Butt six months later and arrested him. Butt was then let off with a caution.