UK terror threat level increased to critical in wake of Manchester Arena attack investigation
The last time that the UK threat level was critical was June 30 2007 - in the wake of the Glasgow airport car bombing.
The only time before that it was raised to critical - the highest possible level - was on June 30 2006 when a plot to kill thousands on 10 transatlantic flights from the UK was uncovered.
Anti-terror agencies have been working for the past 24 hours to work out if the suicide bomber who killed 22 and injured 120 more at the Ariana Grande pop concert last night was working alone - or as part of an organised terror cell....