Shortly after UK police identified 22-year-old Salman Abedi as the suspected suicide bomber who detonated bombs on Monday evening at the Ariana Grande concert in Manchester which killed 22 people, Prime Minister Theresa May announced that the UK has raised its threat level to "critical".
This is the highest level for the first time in a decade. The last occasions were in August 2006 and June 2007. Both times, the assessment was lowered after a few days.

Raising the threat level to a critical level suggests that intelligence services believe another attack is "imminent."
According to Theresa May, the Joint Terrorism Analysis Centre - the independent body which sets the threat level - had recommended it be raised after the Manchester bombing.  She said:

"It is now concluded on the basis of today's investigations that the threat level should be increased for the time being from severe to critical.  This means that their assessment is not only that an attack remains highly likely but that a further attack may be imminent."