“Given the nature of the attack, it is likely that the suspect was part of a cell.  If so, he may not have been the bomb maker.  If so, again, the hunt for other members of that cell will be intense…And since he indeed was known to the authorities, and seems not to have been a “lone wolf” but part of a cell, we must be ready for further twists in this horrible story.”

So we wrote earlier this evening, and it is in this direction that events are moving.

Theresa May has now announced that the threat level has been raised from “severe” to “critical” – the most serious one.  It means that “an attack is expected imminently”.  The five threat levels are designed to give “a broad indication of the likelihood of a terrorist attack”.  They are set not by the Prime Minister, but by the Joint Terrorism Analysis Centre, which sits within MI5.

This level appears automatically to have kicked in Operation Temperer.

This sees troops take over armed police patrol duties under police command.  Some 5000 will apparently be deployed.  It means, in the Prime Minister’s words, that “armed police officers responsible for duties such as guarding key sites will be replaced by members of the armed forces, which will allow the police to significantly increase the number of armed officers on patrol in key locations”.

Troops will also be “deployed at certain events, such as concerts and sports matches” under police command.

The threat level has only been raised to critical twice previously since the system was introduced in 2006.  This is the first time that it has been increased to Critical since 2007, when it was held at that level for only a few days.  It is clear from briefing that the level has been raised to the highest possible because the security services believe that Salman Abedi may not have acted alone – or else have specific information.