In a televised statement from Downing Street, UK PM Theresa May said Britain has increased its security threat level to the highest possible "critical" from "severe", following Monday's suicide attack in Manchester that killed 22 people, and she also said members of the army would be positioned at key sites to free up police for patrols and military personnel might be deployed at public events such as concerts and sports events as a further attack was seen as potentially imminent.
“Members of the armed forces deployed in this way will be under the command of police officers,” May said, adding that "we cannot ignore that there is a wider group of individuals linked to Manchester attack".
The Prime Minister also said the independent body which sets the threat level had recommended it be raised from "severe" after a man named by police as Salman Abedi set off an improvised bomb on Monday night as crowds streamed out of a concert.
"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," she said in a televised statement following a meeting of the government's crisis response committee. This means that their assessment is not only that an attack remains highly likely but that a further attack may be imminent."
May continued: "I do not want the public to feel unduly alarmed. "We have faced a serious terror threat in our country for many years and the operational response I have just outlined is a proportionate and sensible response to the threat that our security experts judge we face.
"I ask everybody to be vigilant and to co-operate with and support the police as they go about their important work.
"I want to end by repeating the important message I gave in my statement earlier today. We will take every measure available to us and provide every additional resource we can to the police and the security services as they work to protect the public.
"And while we mourn the victims of last night's appalling attack, we stand defiant. The spirit of Manchester and the spirit of Britain is far mightier than the sick plots of depraved terrorists, that is why the terrorists will never win and we will prevail."
May, who is facing a national election in two weeks, said the man named by police as the attacker, Salman Abedi, was born and brought up in Britain and investigations into whether he was working alone were ongoing.
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Britain’s threat level has been at the “severe” level since 2014. It has only been at a “critical” level twice before, in 2006 and 2007 (see table below). May said the independent body which sets the threat level had recommended it be raised after a man named by police as Salman Abedi set off an improvised bomb on Monday night as crowds streamed out of a concert.