Theresa May warns a fresh terror attack is feared to be IMMINENT as she raises threat level to critical and orders 5,000 troops onto the streets after attack

• Troops are to be deployed onto Britain's streets amid fears a further terror attack 'may be imminent'
• Theresa May announced the move this evening, less than 24 hours after the bomb attack at a teen concert
• Prime Minister confirmed the identity of the Manchester suicide bomber as British Libyan Salman Abedi, 22

Troops are to be deployed onto Britain's streets amid fears a further terror attack 'may be imminent'.

Theresa May announced the move this evening, less than 24 hours after the bomb attack at a teen concert in Manchester, which left 22 dead and 59 injured.

The Prime Minister confirmed the identity of the Manchester suicide bomber as 22-year-old British Libyan Salman Abedi.

But intelligence agencies fear he may not have acted alone - leaving open the possibility of an active Islamist terror cell on the loose.

Britain's Joint Terrorism Analysis Centre last night raised the terror threat level to 'critical', its highest level. 

The threat level has only been raised to 'critical' twice since the system was introduced in August 1, 2006. 

It came after the worst UK atrocity since 2005, when a nail bomber murdered 22 concert-goers as young as eight at an Ariana Grande concert.

The suicide bomber Abedi, a Mancunian of Libyan descent, was the son of an airport security worker, MailOnline can reveal.

Police today carried out a controlled explosion at the doorstep of his home during raids around the city. 

Police also raided a house where Abedi's brother, Ismail, lived and arrested a 23-year-old man, prompting speculation that Ismail had been detained. 

curity services are trying to establish whether Salman worked alone or was part of a wider network that helped him with the bomb.  

Speaking inside Downing Street following a meeting of the emergency committee Cobra, Mrs May said: 'Earlier today I said the security services needed to investigate whether Abedi was working alone and these investigations continue.  

'It is a possibility we cannot ignore that there is a wider group of individuals linked to this attack. 

'The joint terrorist analysis centre has concluded 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 a further attack is imminent.'  

It means armed soldiers will patrol key sites across the country, at sporting fixtures and musical events.

Undercover SAS troopers will join regular soldiers in Operation Temperer. 

She added: 'We don't want the public to feel unduly alarmed. We've faced a serious terrorist threat in this country for many years.'

She said the response was 'proportionate and sensible'.

The Prime Minister said: 'The liberal pluralistic values of Britain will always prevail over the hateful ideology of the terrorists. They proved that cowardice will always be defeated by bravery.'

Mrs May closed her statement saying the spirit of Manchester and Britain as a whole showed the terrorists would not win, and branded atrocities such as last night's 'sick plots'.

She said: 'That's why the terrorists will never win, and we will prevail.'  

Tonight's announcement comes after ISIS claimed responsibility for the worst terror attack Britain has seen since the 7/7 London bombings.

The suicide bomber, Salmon Abedi, was known to the security services but was not part of any active investigation or regarded as a high risk.

He died at the scene and police today carried out a controlled explosion at his home as chemical experts were seen outside with specialist instruments to check the property for traces of chemicals or explosives. 

TERROR THREAT LEVEL RAISED TO 'CRITICAL'

Just one week after its launch, the levels were raised to critical when police uncovered a plot to smuggle explosives on passenger jets travelling between the UK and US.

There was a fresh state of heightened alert in June 2007 when a blazing car loaded with propane cannisters was driven into Glasgow Airport. 

Critical is the highest threat level under the system which is 'designed to give a broad indication of the likelihood of a terrorist attack'. Low means an attack is unlikely while moderate means an attack is possible, but not likely. Moving up the scale, substantial means an attack is a strong possibility while severe means an attack is highly likely. 

The highest level - critical - means an attack is expected imminently.

The threat level for the UK from international terrorism is set by the Joint Terrorism Analysis Centre (JTAC). MI5 is responsible for setting the threat levels from Irish and other domestic terrorism both in Northern Ireland and in Great Britain. 

In reaching a judgement on the appropriate threat level in any given circumstance several factors need to be taken into account. These include judgements about the threat 'based on a wide range of information' including the nature of current terrorist activity and events in other countries.

Police were last night also quizzing his brother Ismail, 23, on suspicion of involvement in the bombing. 

Abedi was born in Manchester on New Year's Eve 1994, the son of two Libyans who came to Britain to escape the Gaddafi regime. 

His father, Ramadan Abedi, is a former airport security worker, MailOnline can reveal. 

It is understood he has three siblings, two brothers, Ismail and Hashem and a sister, Jomana.   

The suicide bomber was heard chanting Islamic prayers in Arabic just weeks before the attack, a neighbour has revealed.    

Lina Ahmed, 21, told MailOnline: 'They were a Libyan family. A couple of months ago he [Salman] was chanting the first kalma [Islamic prayer] really loudly in the street.

 He was chanting in Arabic. He was saying 'There is only one God and the prophet Mohammed is his messenger.'

Salman and his brother Ismail worshipped at Didsbury mosque, where their father is a well-known figure. 

Ramadan is thought to be in Tripoli. His wife, Samia, is undestood to be in Manchester.

Some were shocked by Salman's involvement in the terror attack.

 One member of Manchester's Libyan community told the Guardian: 'Salman? I'm astonished by this. He was such a quiet boy, always very respectful towards me. His brother Ismail is outgoing, but Salman was very quiet.

 He is such an unlikely person to have done this.'

However others had a different recollection of the 22-year-old. Mohammed Saeed, the imam of Didsbury Mosque and Islamic Centre, said Salman Abedi had looked at him 'with hate' after he gave a sermon attacking ISIS and Ansar al-Sharia in Libya. 

He said a friend was so concerned that he got his adult children to sit beside Salman Amedi in case he attacked the imam.

Leon Hall, who went to school with Abedi, told MailOnline he saw the killer last year and said he had grown a beard. He also said the jihadist was a keen Manchester United fan. 

Mr Hall said: 'I saw him last year and he had a beard thing going on. We didn't speak but just nodded to each other. I don't remember seeing him with beard before.'

'He always had a bit of an attitude problem. I can't say I really liked the man.'

Mr Hall said Abedi lived in a housing association owned home about two miles from the scene of Monday night's terror attack.

Three of the 22 victims have been named as college student Georgina Callander, eight-year-old schoolgirl Saffie Roussos, 26-year-old John Atkinson, Kelly Brewster and primary school pupil Megan Hurley.  

The headteacher of the school of the youngest victim named so far, Saffie Roussos, said she was 'simply a beautiful little girl in every aspect of the word'.

Tracey Radcliffe, a leader at 1st Tarleton Brownies, added: 'Saffie was an adorable and lovable little girl - she really was.

'I didn't know her parents, but she was just lovely. No one should go to a gig and not return.'

A close friend of victim Georgina Callander said she died in hospital with her mother at her bedside in hospital.

Another friend tweeted: 'A beautiful girl with the kindest heart & soul, I'll miss you forever, may you rest in a better place than here. I love you.' 

Victim Mr Atkinson, from Radcliffe, was leaving the concert at the venue when it was targeted by the suicide bomber.

Friends and family have paid their respects online, describing him as an 'amazing young man'.

Lee Paul posted on Facebook: 'Sleep tight John Atkinson. Thoughts and prayers with all your family and the other 21 people who lost there lives last night.'

Tracey Crolla wrote: 'Thinking of all the Atkinsons at this very sad time John Atkinson you turned into an amazing young man so kind and thoughtful you will be missed by everyone x x.' 

WHAT IS OPERATION TEMPERER? 

Documents uncovered by The Mail on Sunday in July 2015 revealed that the operation, codenamed Operation Temperer, would see 5,000 heavily armed troops deployed.

The unprecedented operation would see troops guard key targets alongside armed police officers, providing 'protective security' against further attacks, while counter-terror experts and MI5 officers hunted down the plotters. 

At the time the documents emerged, Baroness Jones, who sits on London's Police and Crime Committee, said she was 'shocked' at the plans, saying: 'This would be unprecedented on mainland Britain.' 

And she expressed concern that the troops would not be sufficiently trained to protect civil liberties.

The paper says up to 5,100 military personnel could be deployed 'based upon force assessments of how many military officers could augment armed police officers engaged in protective security duties'.  

SAS DROOPS DRAFTED INTO MANCHESTER AS PM CONSIDERS PUTTING ARMED SOLDIERS ON STREETS 

SAS troops were drafted into Manchester yesterday to support the police as counter terror officers launched a major operation to find friends and relatives of the suicide bomber.

The 20 strong heavily armed team were flown north as part of a contingency plan to counter any surge in extremist violence - such as a hostage situation - that will require military intervention.

Under the direction of the Counter Terrorist Command the soldiers, many of who have worked with specialist police unit in the past few years, were on standby to join undercover teams and armed response units deployed in the city.

The move came as Air Marshall Sir Stuart Peach, the head of the UK's armed forces, told a Cobra meeting that the military was ready to put armed soldiers on the streets if directed by the Prime Minister.

As part of an ongoing high readiness response, codenamed Op Temperer, Army commanders have three infantry battalions of armed soldiers ready to deploy anywhere across the country to support the police.

The Prime Minister is understood to be reviewing a wider intelligence assessment from officers at the Joint Terrorist Analysis Cell, before making any decision on the deployment of armed soldiers on mainland Britain.

The rotation of available soldiers changes on a regular basis with paratroopers from 16 Air Assault Brigade currently listed as the 'in role' force ready to provide additional public security.