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Soldiers have been sent on to Britain’s streets to help the police following the Manchester terrorist attack which killed at least 22 people including several children and wounded dozens.  Prime Minister Theresa May raised the threat level from severe to critical for the first time since July 2007, meaning “not only that an attack remains highly likely but a further attack may be imminent”.

May said she did not want to “unduly alarm” people but military personnel would be present at public events and key sites under police command, according to theguardian.com.

She said it could not be ruled out that the attacker, named as Salman Ramadan Abedi, was working as part of a terrorist group.

Speaking after an emergency Cobra (the cabinet emergency response committee) meeting, May said the investigations have “revealed it is a possibility we cannot ignore that there is a wider group of individuals linked to this incident”. The prime minister said: “The police have asked for authorisation from the secretary of state for defence to deploy a number of military personnel in support of their armed officers.”

This means some armed police officers guarding events will be replaced by soldiers in an operation codenamed Temperer. It is the first time that the operation, which was first revealed in 2015, has been put into effect. The plan is believed to allow up to 5,000 troops to be deployed in support of the police, replacing armed officers at many sites to free them up for patrols in key areas.

Police and security services are seeking to establish if the assailant was acting on his own or was linked to a wider organisation. The investigation was understood to be focusing on whether Abedi was directly supported by other conspirators or built the bomb himself to instructions obtained over the internet. The device he used was described as homemade and crude although it was stable enough to be transported, and exploded with devastating effect. It was believed to have been constructed in Britain.

One senior security source described Abedi’s attack involving the acquisition of bomb-making materials or the construction of a viable device as “a game-changer” that has “rocked us backwards”, because a successful bomb plot has not been seen in the UK since the 7/7 attacks in 2005.

Investigators have gathered CCTV footage showing Abedi approaching the foyer in the MEN Arena, which conclusively shows the explosion was deliberate and caused by a suicide device. He was also carrying ID on him when he detonated the bomb.