The government has raised its security threat level from "severe" to "critical" following the suicide bombing at a concert in Manchester which killed 22 people. There are five threat levels - low, moderate, substantial, severe and critical - set by the Joint Terrorism Analysis Centre (JTAC) based at the Security Service (MI5). The "critical" threat level means military personnel will now be deployed to protect key sites. The change in terror threat comes after investigators were unable to rule out whether the bomber, named by police as Salman Abedi, was part of a cell. The Islamic State (IS) said one of its members carried out the attack.

The highest threat level has only been reached twice before. The first time the threat level was raised to critical was in 2006 during a major operation to stop a plot to blow up transatlantic airliners with liquid bombs. The following year, the government raised it once more as police searched for the men who had tried to detonate a car bomb outside a London nightclub, before going on to attack Glasgow Airport. Both times the level was reduced after a few days.  Prime Minister Theresa May has suggested that this time it could last several weeks. The attack in Manchester was well planned and likely involved more than one perpetrator. 

Up to 3,800 soldiers are to be deployed as part of Operation Temperer. The plan was created after the November 2015 Paris attack, which saw three teams launch six distinct assaults and kill 130 people. Prime Minister May announced that the police had asked for military support and the request had been approved by Sir Michael Fallon, the Secretary of State for Defense. The move to deploy soldiers highlights the difficulty of protecting soft targets - places where terrorists can target undefended and unaware civilians. Such soft targets include hotels, bars, restaurants, sports bars and nightclubs, sporting events, shopping centres and transport hubs. Operation Temperer allows soldiers to replace armed police so that a wider security zone around a certain venue can be established or officers can be deployed to other key areas.

Reports indicate the British military is also playing an active role in counter-terrorism efforts. The authorities believe that other accomplices of the Manchester bomber are still at large - potentially with access to explosives or other weapons. It is almost certain that UK Special Forces, including the counter-terrorism unit of the SAS, are on standby to support the police. Security planners hope an increased number of special forces operatives in strategic areas will potentially neutralize or contain terrorists conducting an attack, and thus limit deaths and injuries inflicted. It is highly likely that more intelligence operators have been tasked to carry out surveillance on high-risk terror suspects. More assets have probably been deployed overseas to get further upstream of any identified threats given the reports that Abedi had travelled to Libya and Syria. 

Authorities will almost certainly increase security at public events, such as the FA Cup Final at Wembley Stadium on 27 May, the Chelsea Flower Show, running from 23 May to 27 May, the Rugby Premiership Final at Twickenham on 27 May, and the UEFA Champions League Final in Cardiff on 3 June. Since the access to the venues themselves will be protected by security checks and armed personnel, it is more likely that perpetrators would attempt to attack elsewhere, where large groups of people are exposed and unprotected. Even if event organizers opt to establish a wider security zone around a certain venue, the risk of an attack is still elevated on streets connecting the venue with transport hubs. For this reason, Operation Temperer will be used to plug security gaps and free up the police to patrol key areas.

The risk of further attacks remains elevated by both lone actors inspired by IS propaganda as well as individuals or cells with more direct contact and operational support from the group. Strict gun control laws in the UK and a strong control over borders means that low-capability weapons like vehicles or knives, rather than military-grade firearms, will remain the more likely terrorist attack options. The use of improvised explosive devices, including suicide variants, is also likely to be a favored attack option. There is also a risk of more coordinated attacks by small cells that could include terrorists who have fought in conflict zones such as Syria and Iraq.

This attack happens just a few weeks after the U.S. State Department issued a warning for Europe-wide travels. For more information about this Travel Warning, click here.