The security services were facing difficult questions last night over how at least one of the London Bridge terrorists slipped through the intelligence net.It emerged that the 27-year-old Muslim extremist known to friends as 'Abz' appeared in a TV documentary last year about British jihadis – and was involved in a filmed altercation with police after an ISIS flag was unfurled in Regent's park, London.He was caught on camera alongside two notorious preachers who were well known to police and intelligence officials because of their extremist views.Amid a series of revelations last night, it was claimed that a friend of...