The UK terror threat level has been raised from severe to critical - the highest possible - after the Manchester Arena bombing.

The move indicates that another attack could be "imminent", as well as "highly likely".

After chairing a meeting of the Government's emergency COBRA committee, Theresa May announced the change, saying military personnel will help armed police officers guard key sites.

:: LIVE: The latest updates on the Manchester attack from the Sky News team

Image: Thousands of people gathered in Manchester for a vigil commemorating the victims of the terror attack at the city's arena Image: Many waved placards to show their support Image: Former Lancashire cricketer Andrew 'Freddie' Flintoff was among those who attended Image: Poet Tony Walsh read out his poem This Is The Place - Forever Manchester Image: Greater Manchester Police's Ian Hopkins described the crime as 'unthinkable' Image: Home Secretary Amber Rudd (L), Labour leader Jeremy Corbyn (C) and Lib Dem leader Tim Farron (R) took part Image: Crowds spilled from Albert Square on to nearby roads, standing together in an act of solidarity Image: Many thanked the emergency services for the speed at which they responded to the attack Image: This t-shirt worn by a young woman who attended was her own ode to Manchester Image: People gave out food to those attending the vigil in Manchester's Albert Square Image: The city was joined by people paying their respects in London Image: Two members of Muslim Aid were among those showing support in Manchester Image: A member of Manchester's Syrian community attended to pay her respects and show solidarity Image: Scroll through for more pictures... /

Under Operation Temperer, members of the armed forces could be deployed to public events, such as concerts and sports events, and also on the streets and at major shopping centres.


Twenty-two people were killed and 59 others injured when a bomber blew himself up in the arena foyer as thousands of concertgoers were leaving after a gig by US pop star Ariana Grande.

The suspect has been named by police as Salman Abedi, and investigations have revealed he may not have acted alone.

Islamic State has claimed it carried out the attack, which involved a homemade device packed with nuts and bolts.

:: Eight-year-old Saffie Roussos named as Manchester bomb victim

Image: Helpers attend to people inside the arena after the blast

The Prime Minister said the possibility "that there is a wider group of individuals linked to this attack" could not be ignored.

Mrs May said the Joint Terrorism Analysis Centre - the independent body which sets the threat level - had recommended it be raised after the bombing on Monday evening.

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."

:: Singer Ariana Grande 'broken' by bombing of young fans

What is Operation Temperer?

Assistant Commissioner Mark Rowley, head of national counter-terrorism policing, said the investigation was "making good progress".

He said: "There has been an arrest and there are currently multiple searches and other activity taking place as I speak.

"The public would expect the police to do everything possible to prevent further attacks and keep them safe.

"We are flexing our resources to increase police presence at key sites, such as transport and other crowded places and we are reviewing key events over the coming weeks."

:: Bomb attack witness: 'It was absolute carnage'

Suicide bomber suspect named as Salman Abedi

Following the increase to the threat level, all the major political parties have cancelled General Election campaigning for a second day.

It is not yet known how long the suspension - which covers campaigning on both a local and national level - will last.

This attack is the worst terrorist incident ever during a general election period.

It is the first time in a decade that the terror threat level has been at critical.

Who were the victims of the Manchester attack?

The last occasions were in August 2006 and June 2007, the latter following the Glasgow airport attack. Both times, the assessment was lowered after a few days.

Police investigating the arena attack have arrested a 23-year-old man.

Threat levels are designed to give a broad indication of the likelihood of a terrorist attack.

:: LOW means an attack is unlikely

:: MODERATE means an attack is possible, but not likely

:: SUBSTANTIAL means an attack is a strong possibility

:: SEVERE means an attack is highly likely

:: CRITICAL means an attack is expected imminently

:: A hotline has been set up for those with concerns about loved ones who remain unaccounted for. Those worried about their friends or family should call 0800 096 0095.