Members of the terrorist network which carried out the Manchester atrocity may have fled to elsewhere in Britain and could have access to bomb-making material, according to security sources. Smaller towns which may not have a large armed police presence are places of particular concern.

The police and security agencies had attempted, with a large measure of success, to uncover the cell which helped Salman Abedi carry out the mass murder.

In the early hours of Saturday morning, Greater Manchester Police officers arrested two more men, aged 20 and 22, and carried out a controlled explosion during a series of raids in the Cheetham Hill area of the city. In the Moss Side area, residents were evacuated as police carried out a major search linked to the investigation. Eleven suspects are now in custody in all and evidence, including components of explosive devices, has been recovered.

But the apprehension that a few of Abedi’s accomplices have managed to escape the net and may attempt to strike in another part of the country lies behind the deployment of troops across the country. The threat level being kept at its highest classification, critical, and members of the SAS being used to carry out raids in case of resistance using firearms. Special operational measures are in place to take action if necessary away from large metropolitan centres, as was seen in the arrest of one of a suspect at Nuneaton, in Warwickshire.

A senior counter-terrorism officer, Assistant Commissioner Mark Rowley, stated that the police have “got hold of a large part” of the terror network. Security has been reviewed at 1,300 events across the country, he said, and urged the public to “go out as you planned and enjoy yourself” over the Bank Holiday weekend. Events such as Radio 1's Big Weekend in Hull got under way on Saturday with the visible presence of armed police officers at entrance points.

But, Mr Rowley added that there still “important” lines of inquiry to pursue, more arrests were likely, and acknowledged that security status needs to remain at critical, for possibly as long as few more weeks.

The Independent revealed two days ago that a quantity of bomb-making material, including explosives, known to have been in possession of 22-year-old Abedi, of Libyan background, and others in the group is missing and not all of it has been found despite extensive searches.

Armed police officers patrol outside Burton Constable Hall in Hull on Saturday ahead of BBC Radio 1's Big Weekend (PA)

The Chief Constable of Greater Manchester, Ian Hopkins, said: “It has been an extremely challenging week, and we are still in the middle of the investigation. We have seized thousands of exhibits which are now being assessed. I think it is fair to say there have been enormous progress with the investigation, but there is still an awful lot of work to do”.

One of the raids today took place at a barber shop in Moss Side which is believed to be owned by a cousin of Abedi, believed to be called Abdallah Forjani. A 38-year-old man who rented a flat to Abedi in the Blackley area is being held.

Abedi left the flat in March to travel to Libya. His father, Ramadan Abedi, also known as Abu-Ismail al-Obedei, is a former member of the Libyan Islamist Fighting Group ( LIFG) an extremist organisation which was banned by the UN for its links to al-Qaeda after the 9/11 attacks in New York. Ramadan Abedi and a son, Hashem, 20, have been arrested in Tripoli by a militia affiliated to the country’s UN backed government. Another son, Ismail, 24, was arrested and remains in custody in England.

Manchester explosion in pictures Show all 37 1 /37 Manchester explosion in pictures Manchester explosion in pictures People running down stairs as they attempt to exit the Manchester Arena after a blast, where U.S. singer Ariana Grande had been performing, in Manchester Twitter/@ZACH_BRUCE/ via REUTERS Manchester explosion in pictures Helpers attend to people inside the Manchester Arena after a suspected suicide bomber detonated an explosive device at the end of an Ariana Grande concert, killing 22 people PA wire Manchester explosion in pictures Armed officers guard outside a hotel near the Manchester Arena following reports of an explosion, in Manchester, Britain EPA Manchester explosion in pictures Police officers are seen outside the Manchester Arena, where U.S. singer Ariana Grande had been performing, in Manchester, northern England Reuters Manchester explosion in pictures MANCHESTER, ENGLAND - MAY 23: Police escort members of the public from the Manchester Arena on May 23, 2017 in Manchester, England. An explosion occurred at Manchester Arena as concert goers were leaving the venue after Ariana Grande had performed. Greater Manchester Police have confirmed 19 fatalities and at least 50 injured. (Photo by Christopher Furlong/Getty Images) Getty Images Manchester explosion in pictures MANCHESTER, ENGLAND - Emergency services arrive close to the Manchester Arena on May 23, 2017 in Manchester, England. There have been reports of explosions at Manchester Arena where Ariana Grande had performed this evening. Greater Manchester Police have have confirmed there are fatalities and warned people to stay away from the area. (Photo by Dave Thompson/Getty Images) Getty Images Manchester explosion in pictures MANCHESTER, ENGLAND - MAY 23: Police escort members of the public from the Manchester Arena on May 23, 2017 in Manchester, England. An explosion occurred at Manchester Arena as concert goers were leaving the venue after Ariana Grande had performed. Greater Manchester Police have confirmed 19 fatalities and at least 50 injured. (Photo by Christopher Furlong/Getty Images) Getty Images Manchester explosion in pictures Medics deploy at the scene of a reported explosion during a concert in Manchester, England on May 23, 2017. British police said early May 23 there were "a number of confirmed fatalities" after reports of at least one explosion during a pop concert by US singer Ariana Grande. Ambulances were seen rushing to the Manchester Arena venue and police added in a statement that people should avoid the area / AFP PHOTO / Paul ELLIS (Photo credit should read PAUL ELLIS/AFP/Getty Images) AFP/Getty Images Manchester explosion in pictures Police and fans close to the Manchester Arena, after reports of an explosion Getty Images Manchester explosion in pictures There have been reports of explosions at Manchester Arena where Ariana Grande had performed Getty Images Manchester explosion in pictures Police deploy at scene of explosion in Manchester, England, at a concert in Manchester Arena AFP/Getty Images Manchester explosion in pictures Police stand by a cordoned off street close to the Manchester Arena Getty Images Manchester explosion in pictures Police deploy at scene of explosion in Manchester, England AFP/Getty Images Manchester explosion in pictures Police deploy at scene of a reported explosion during a concert in Manchester, England, on May 23, 2017. British police said early May 23 there were "a number of confirmed fatalities" after reports of at least one explosion during a pop concert by US singer Ariana Grande. Ambulances were seen rushing to the Manchester Arena venue and police added in a statement that people should avoid the area AFP/Getty Images Manchester explosion in pictures An ambulance drives away from the Manchester Arena, where U.S. singer Ariana Grande had been performing, in Manchester Reuters Manchester explosion in pictures Police escort members of the public from the Manchester Arena in Manchester, England. Getty Images Manchester explosion in pictures A woman sits in the street in a blanket near the Manchester Arena as police guard the area following reports of an explosion, in Manchester, Britain EPA Manchester explosion in pictures Two women wrapped in thermal blankets stand near the Manchester Arena, where US singer Ariana Grande had been performing, in Manchester Reuters Manchester explosion in pictures A Royal Logistic Corps (RLC) bomb disposal robot is unloaded outside the Manchester Arena following reports of an explosion, in Manchester. At least 19 people have been confirmed dead and others 50 were injured, authorities said. It is being treated as a terrorist incident until police know otherwise EPA Manchester explosion in pictures A Royal Logistic Corps (RLC) bomb disposal robot is unloaded outside the Manchester Arena following reports of an explosion, in Manchester EPA Manchester explosion in pictures Members of the public receive treatment from emergency service staff at Victoria Railway Station close to the Manchester Arena on May 23, 2017 in Manchester, England. There have been reports of explosions at Manchester Arena where Ariana Grande had performed this evening. Greater Manchester Police have have confirmed there are fatalities and warned people to stay away from the area Getty Images Manchester explosion in pictures Armed police after a suspected terrorist attack at the Manchester Arena at the end of a concert by US star Ariana Grande left 19 dead PA wire Manchester explosion in pictures Emergency services arrive close to the Manchester Arena in Manchester Getty Images Manchester explosion in pictures An amoured police vehicle patrols near Manchester Arena in Manchester Getty Images Manchester explosion in pictures A man carries a young girl on his shoulders near Victoria station in Manchester AFP/Getty Images Manchester explosion in pictures Police officers stand at the Miller Street and Corporation Street Crossroads, in front of the Manchester Arena in Manchester, England Getty Images Manchester explosion in pictures Police block a road near to the Manchester Arena in central Manchester, England AP Manchester explosion in pictures Armed police patrol near Victoria station in Manchester, northwest England. Twenty two people have been killed and dozens injured after a suspected suicide bomber targeted fans leaving a concert of US singer Ariana Grande in Manchester Getty Images Manchester explosion in pictures Police forensic officers leave the Manchester Arena as they investigate the scene of an explosion in Manchester Getty Images Manchester explosion in pictures A forensic officer collects evidence on a walkway between Victoria station and Manchester Arena following a deadly terror attack in Manchester, Getty Images Manchester explosion in pictures A woman and a young girl wearing a t-shirt of US singer Ariana Grande talks to police near Manchester Arena following a deadly terror attack in Manchester, Getty Manchester explosion in pictures epaselect epa05982725 Susan Walton and daughter Katie, 10 (pictured), who attended the concert of Ariana Grande at the Manchester Arena, are seen in Manchester, Britain, 23 May 2017. According to a statement released by the Greater Manchester Police on 23 May 2017, police responded to reports of an explosion at Manchester Arena on 22 May 2017 evening. At least 19 people have been confirmed dead and around 50 others were injured, authorities said. The happening is currently treated as a terrorist incident until police know otherwise. According to reports quoting witnesses, a mass evacuation was prompted after explosions were heard at the end of US singer Ariana Grande's concert in the arena. EPA/NIGEL RODDIS EPA Manchester explosion in pictures Mayor of Greater Manchester Andy Burnham and Manchester City Council Leader Sir Richard Leese speak to the media outside Manchester Town Hall after a suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester Dave Higgens/PA Wire Manchester explosion in pictures The media gather behind a police cordon in Manchester Getty Images Manchester explosion in pictures Flowers left close to the Manchester Arena, the morning after a suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester Danny Lawson/PA Wire Manchester explosion in pictures Ariana Grande concert attendees Karen Moore and her daughter Molly Steed, aged 14, from Derby, leave the Park Inn where they were given refuge after last night's explosion at Manchester Arena Getty Manchester explosion in pictures Signs saying 'We love Manchester' are displayed in a window in Manchester, England Getty Images

The security agencies are investigating whether Salman Abedi was indoctrinated during various visits to Libya. However there are suggestions that he had become radicalised in Manchester over a prolonged period. A mosque in Didsbury where Ramadan Abedi used to lead the call to prayers and Salman Abedi attended, has become a focus of attention.

Members of the mosque’s congregation and its trustees have denied any extremist link and have condemned the Manchester attack. But there is evidence that hardline Islamists, including members of militia in Libya, have attended the mosque. A speaker featured on the mosque's official YouTube channel “described martyrdom as virtuous”.

There had been suggestions that Salman Abedi had also travelled to Syria. The French foreign minister, Gerard Collomb, claimed that the British security agencies believe he went on to Syria from Libya. But a senior security source said: “We think he got a few things garbled there, we know that Abedi had gone to Libya, whether he went to Syria or not remains a line of inquiry.”