Jonathan Russell is head of policy at Quilliam, a counter-extremism organization based in London. The opinions in this article belong to the author.
What can governments actually do to stop terror?
Independently set by the Joint Terrorism Analysis Centre (JTAC), "Critical" means an attack from jihadist terrorism is expected imminently. It also means that Operation Temperer, which allows up to 5,000 military personnel to support the police on British streets, will be activated for the first time.
This is a point of departure for Britain. Prime Minister Theresa May has reminded the British public to remain vigilant, but has insisted that she doesn't wish for people to be unduly alarmed.
What affect will this have? Can Britain learn from other countries that have taken similar approaches before? And what more needs to be done to keep Britons safe?
The first question is one of resourcing and reassurance. Freeing up the police to investigate the network that possibly surrounds the attacker Salman Abedi, follow various intelligence leads and prevent copycat attacks from occurring is certainly a positive step.
We know from research that ISIS directs, enables and inspires attacks in the West, but very rarely takes a micro-managing command and control role for fear of being rumbled.
The presence of armed British troops will put off the perpetrators of future attacks from immediately carrying out their plans and give the police and intelligence services much needed time to follow precious leads.
Additionally, the visible presence of "good guys with guns" on British streets will reassure understandably afraid members of the public that the security forces holds the upper hand against the perceived presence of "bad guys with guns." The country needs leadership and both anger and frustration are rising at the powerlessness of the state against these asymmetric threats.
Comparisons will be made with France, which has been in a State of Emergency since the Paris attacks in November 2015. This gives the authorities more powers, including forbidding mass gatherings, setting curfews, increasing surveillance, closing public spaces that may present soft targets for terrorists and conducting house searches without judicial oversight.
This is a considerable step up from the measures currently in place in Britain and the provision has been renewed five times, extending beyond the 12 days that it was initially in place for. Indeed, it has been extended again in France following the Manchester attack.
Likewise, following 9/11, the US declared a National Emergency, thereby suspending certain provisions that limit the size of the military. This has been renewed by successive administrations and supplemented by the Patriot Act and various extensions, which enables wiretaps, surveillance of potential lone actor terrorists and searches of business records.
The question, in both cases, is whether these measures are effective at stopping terrorism.
It is very hard for us to prove a negative -- that these measures have prevented an otherwise imminent attack. Likewise, we must wonder if extension, as has been the case in both France and the USA, is inevitable and whether the renewal of temporary and emergency measures indefinitely poses a threat to our civil liberties.
Israel has been in a State of Emergency since 1948, and some elements of its "normal" constitution have never been in place. Is the threat posed by jihadists to us all so great, that this is the new normal now?
Just as in with these other countries, Britain faces a large number of potential terrorists -- indeed, more than the security services can afford to monitor around the clock. It also has an inordinate number of "soft" targets.
It is not just Ariana Grande concerts that attract 20,000 attendees. On any single Saturday of the year, there are likely 50 sports stadiums with more than 20,000 people inside. The security infrastructure that goes into physically guarding these locations dovetail with the signals intelligence provided by the security services to triage the most vulnerable targets and use resources most effectively, but even then they are understandably overstretched.
This is why new laws and emergency provisions will ultimately fall short.
The authorities need the help of the public to be aware and to report suspicious activity or behavior when they see it. Only then does the numbers game start to be loaded in our favor.
This is where approaches in countries like Singapore work particularly well. Their new SGSecure App acts as a public warning system, raising awareness and providing training, as well as being a one-stop portal for the public to send useful information to the authorities.
Beyond this, the UK Home Secretary Amber Rudd's commitment to uplift Prevent, Britain's program for preventing radicalization, is certainly welcome.
By better resourcing the strategy which aims to make individuals less vulnerable to extremist recruitment and make the public better at preventing radicalization, we can come together practically to reduce the likelihood of another Manchester.