Conditions that allow the activation of Operation Temperer, putting troops on the streets, are agreed at the highest level

The international terrorism threat to the UK has been raised to critical, meaning an attack is expected imminently, in the wake of the Parsons Green bomb attack in London. It is the highest of the five levels used to describe the threat.

Alongside the increased terror threat, phase one of Operation Temperer has been activated, meaning that up to 5,000 armed troops can be deployed at sensitive sites and events, transport hubs and other crowded public places in order to release armed police for other policing duties.



London tube bombing: PM says terror threat level raised to critical Read more

The plan was activated for the first time on 23 May after the Manchester Arena suicide bombing, when the prime minister said the police had asked for military support and the request had been approved by the defence secretary, Sir Michael Fallon.



It is the fourth time the assessment has been raised to critical since the system of official threat levels was introduced on 1 August 2006.



It was last at critical in the wake of the Manchester Arena attack. Before that it was raised for three days from 10 August 2006 at the time of the transatlantic airliner plot, and on 30 June 2007 when the security services uncovered the plot to bomb a nightclub on London’s Haymarket and an attempted car bombing at Glasgow airport.



The threat level is agreed by the Joint Terrorism Analysis Centre based on available intelligence, terrorist capability, terrorist intention and timescale. It was established in June 2003 and is based at MI5’s London headquarters, comprising representatives from 16 government departments and agencies.

On top of the military presence, the Met assistant commissioner Mark Rowley, the UK’s most senior counterterrorism officer, warned the measures “may mean disruption for those who are travelling. The public are asked to be patient and plan ahead, allowing time for delays.”

In total there are five threat levels, with critical the highest.