Manchester attack: Security services think they know who bomber is

Police and security services believe they know the identity of the man behind the Manchester suicide bombing.

Speaking outside Downing Street after chairing a meeting of the Government's emergency COBRA committee, the Prime Minister said authorities are working to establish whether he was acting alone or as part of a group.

Theresa May said the blast at Manchester Arena, which left 22 people dead, was "among the worst terrorism we have experienced in the United Kingdom" and that the city had fallen victim to a "callous terrorist attack".

:: Live updates: 23-year-old man arrested after Manchester suicide bombing

The target was a pop concert, the audience was a mixture of teenagers, many of them young girls, all out for a fun and innocent evening. Some were young enough to need chaperoning by parents or grandparents.

If this does turn out to be an Islamist-inspired attack, the attacker has deliberately targeted everything his warped beliefs hate in a Western society.

He has also demonstrated a deadly competence - he blew himself up as the high-spirited crowd streamed out of the arena after the concert.

The timing, and location of the explosion - just outside the main arena itself - suggests planning and shows he probably carried out a recce.

The singer Ariana Grande is world-famous. She has more than 45 million followers on Twitter. Another basic but twisted way of guaranteeing this attack will resonate far.

:: What we know so far

The morning after the attack, a number of things will be happening simultaneously and with urgency.

In Manchester, counterterrorism police from North West Command will be carrying out forensic work at the scene of the explosion.

They will try and find bomb-making signatures that might give a clue as to who was behind this attack.

They will look for certain chemicals, such as triacetone triperoxide (TATP).

:: Witness: 'It was absolute carnage'

TATP has been used by terrorists around the world, it is a favoured compound of Islamic State and it is relatively straightforward to make, but it is extremely unstable and lethal.